How long does the meetup typically last?
Psychohistorian doesn't say the idea isn't useful, just that reliance on it is incorrect. If the theory is "people mostly do stuff because of signalling", honestly, that's a pretty crappy theory. Once Signalling Guy fails this test, he should take that as a sign to go back and refine the theory, perhaps to
"People do stuff because of signalling when the benefit of the signal, in the environment of evolutionary adaptation, was worth more than its cost."
This means that making predictions requires estimating the cost and benefit of the behavior in advance, which requires a lot more data and computation, but that's what makes the theory a useful predictor instead of just another bogus Big Idea.
Not to point fingers at Freakonomics fans (not least because I'm guilty of this myself in party conversation) but it's real easy to look at a behavior that doesn't seem to make sense otherwise and say "oh, duh, signalling". The key is that the behavior doesn't make sense otherwise: it's costly, and that's an indication that, if people are doing it, there's a benefit you're not seeing. That technique may be helpful for explaining, but it's not helpful for predicting since, as you pointed out, it can explain anything if there's not enough cost/benefit information to rule it out.
Medford, MA. Enjoyed the OB meetup on the MIT campus, which was convenient since I work across the street. I'd be up to renting a car and driving to Amherst or New Hampshire for a meetup on a weekend, especially if there was time for hiking.
Their pages mention that they are funded entirely by donations from past students.
After you've taken the course, how much do they contact you (to solicit donations or otherwise)?