Agreed on most of the above, but on this particular point:

This is pretty much parallel to a common argument for laws against euthanasia, assisted suicide, etc.: the easier it is for someone with terrible medical conditions to arrange to die, [...], or (this isn't quite parallel, but it seems clearly related) to make it appear that they've done so when actually they were just murdered.

I would expect the opposite there.  If assisted suicide and stuff is legalized, I expect that to come with high standards of "There should be a notarized signature, multiple witnesses, a video from the person in question stating their intentions, and they walk into a building where some official people first take the person into another room and say 'Are these men coercing you?  We can have our security staff subdue them and bring in the police'", etc., designed specifically to make it hard to cover up a murder like that.  And the existence of that option should push a chunk of regular suicides in that direction, making it less plausible that someone would commit suicide in the "traditional" way where they give no one any warning, may or may not leave a note, etc.

Yup.  Many programmer applicants famously couldn't solve FizzBuzz.  Which is probably because:

[skipping several caveats and simplifying assumptions]

Now, when you get those 200 resumes, and hire the best person from the top 200, does that mean you’re hiring the top 0.5%?

“Maybe.”

No. You’re not. Think about what happens to the other 199 that you didn’t hire.

They go look for another job.

That means, in this horribly simplified universe, that the entire world could consist of 1,000,000 programmers, of whom the worst 199 keep applying for every job and never getting them, but the best 999,801 always get jobs as soon as they apply for one. So every time a job is listed the 199 losers apply, as usual, and one guy from the pool of 999,801 applies, and he gets the job, of course, because he’s the best, and now, in this contrived example, every employer thinks they’re getting the top 0.5% when they’re actually getting the top 99.9801%.

The Wikipedia link for claddagh rings goes to the Project Semicolon page.

The true thing that Sagan's line might be interpreted to mean is "A claim which is very unlikely on priors needs very strong evidence to end up with a posterior probability close to 1."  "Extraordinary evidence" would ideally have been stated as "extraordinarily strong evidence", but that makes the line a bit clunkier.  Unfortunately, there is often a tradeoff between accuracy and pithiness.  Many pithy sayings require a bit of interpretation/reconstruction to get the correct underlying idea.  I think anyone who invokes a catchphrase should be aware of this, though I don't know how many people share this perspective.

Are there in fact a significant number of people who take it at the face value of "extraordinary evidence" and think it must mean it was obtained via super-advanced technology or something?

I think either I don't know exactly what defines a "subculture", or there needs to be a qualifier before "subculture".  Might "people who are enthusiastic about X sport / hobby / profession" be a subculture?  Because I think lots of those can be highly successful while remaining what they are.  (Perhaps you'd say that hobbies that succeed get eaten in the Geeks/MOPs/Sociopaths way, but that's less so for professions.)

A "subculture of those dealing with X problem" sounds much more likely to fit what you describe, but that may not be your intent.

imagine a friend from a different country is visiting and will stay with you for a while. You're exchanging some text messages beforehand in order to figure out how to spend your time together. You want to show your friend the city, and you want to be very accommodating and make sure all their preferences will be met. So you simply ask them: "What do you want to do"? And maybe you add "I'm completely fine with anything!" to ensure you're really introducing no constraints whatsoever and you two can do exactly what your friend desires.

An additional angle on situations like this: Your friend may be hoping to choose something that's positively enjoyable for you.  Saying "I'm completely fine with anything" may not meet that bar, and doesn't give any hints as to what would.  To illustrate directly, compare "There are ten restaurants nearby and I'm fine with any of them" vs "There are ten restaurants nearby, I've been to them all and I love them all".  I think there are people who would respond to the second with "Great, I'll look them up and pick my favorite" and would find the first frustrating (and may respond by probing, "Well, are there any that you particularly like?"  [And if you really don't care about food, then their hope to find a restaurant you enjoy is destined for frustration.]).

In this case there's also the aspect that, since you live there (likely for some years) and they're from another country, you likely know a lot more about the local offerings than they do (not guaranteed—perhaps you're an ascetic who doesn't explore such things and they're a tourist who has researched your town—but likely), so in a division-of-labor sense it's likely appropriate for you to volunteer info first.

That second aspect is indeed about the pure computational problem.  The first aspect is a combination of the computation/search problem and an emotional negotiation element.

A friend of mine mentioned the article, and here's what I wrote.

Some of it seems pretty unfair. The early anecdote about charity work in Bali seems to be used to criticize the EA ethos, when "rich westerners flying to poor countries to do manual labor (and possibly post on social media about how virtuous they're being)" is the classic case of something EAs consider to be an ineffective and wasteful charity. (Though perhaps EAs might not go so far as to expect it to be net harmful.) I don't think most EAs would agree to the "bet the Earth on a 51% chance" scheme. As the author says, "SBF consistently made terrible choices" even according to SBF's own goals, so I don't think one can point to his bad outcome as evidence that his goals were bad, except perhaps via a psychological argument that having his grand goals and being a powerful player led him to think "good-for-me-now and good-for-everyone-always started to merge into one" (and subsequent self-serving bias), which would be a general argument against having grand goals and being a powerful player.

But the thing of "lots of aid money ends up in the hands of corrupt middlemen and oppressive rulers and might make the whole thing net negative" is a good point; the specific things that went wrong are good to know about; and the thing of GiveWell not taking seriously and honestly the harm caused by the aid (which, given how they operate, would indeed mean publicly writing up calculations) is a very good point. They should take "tracking the negative consequences" into their routine practice; e.g. there exists N such that >$N being given to a cause justifies having a person go and investigate what's happening.

I hadn't checked any of the specific claims about GiveWell's charities going wrong, or about what they have or haven't written about the downsides; I basically took the author's word on that.

Looking at Wiki's Undercover Journalism article, one that comes to mind is Nellie Bly's Ten Days in a Mad-House.

[Bly] took an undercover assignment for which she agreed to feign insanity to investigate reports of brutality and neglect at the Women's Lunatic Asylum on Blackwell's Island. [...]

Once admitted to the asylum, Bly abandoned any pretense at mental illness and began to behave as she would normally. The hospital staff seemed unaware that she was no longer "insane" and instead began to report her ordinary actions as symptoms of her illness. Even her pleas to be released were interpreted as further signs of mental illness. Speaking with her fellow patients, Bly was convinced that some were as "sane" as she was.

Bly experienced the deplorable conditions firsthand. The nurses behaved obnoxiously and abusively, telling the patients to shut up, and beating them if they did not. The food consisted of gruel broth, spoiled beef, bread that was little more than dried dough, and dirty undrinkable water. The dangerous patients were tied together with ropes. The patients were made to sit for much of each day on hard benches with scant protection from the cold. Waste was all around the eating places. Rats crawled all around the hospital. [...]

The bath water was rarely changed, with many patients bathing in the same filthy water. Even when the water was eventually changed, the staff did not scrub or clean out the bath, instead throwing the next patient into a stained, dirty tub. The patients also shared bath towels, with healthy patients forced to dry themselves with a towel previously used by patients with skin inflammations, boils, or open sores.

Interestingly...

While physicians and staff worked to explain how she had deceived so many professionals, Bly's report prompted a grand jury to launch its own investigation[9] with Bly assisting. The jury's report resulted in an $850,000 increase in the budget of the Department of Public Charities and Corrections. The grand jury also ensured that future examinations were more thorough such that only the seriously ill were committed to the asylum. 

I can't say I'm happy with failure being rewarded with a higher budget.  Still, it may have been true that their budget was insufficient to provide sanitary and humane conditions.  Anyway, the report itself seems to have been important and worthwhile.

The ones that come to my mind are "Person or Organization X is doing illegal, unethical, or otherwise unpopular practices which they'd rather conceal from the public."  Lie that you're ideologically aligned or that you'll keep things confidential, use that to gain access.  Then perhaps lie to blackmail them to give up a little more information before finally publishing it all.  There might be an ethical line drawn somewhere, but if it's not at "any lying" then I don't know where it is.