It's a minor annoyance but perhaps I am not the only one who feels this way.
I dislike it when we summarize our posts and articles with a "tl;dr". There's a perfectly good English word for it, namely "summary".
"tl;dr", besides being an ugly internetism, seems to me to convey a certain additional meaning, over the neutral "summary". If, as happens on the rest of the web, a commenter responds to a post with "tl;dr", it expresses an expectation to be entertained without exercising the reader's attention span or making him think. It's also an easy and insulting way to respond to someone you disagree with, avoiding having to process their argument and maybe change your mind.
If an author uses it in their own article, it seems to me to be pandering to the same expectation, apologising for actually having something to say that takes a few paragraphs to explore properly. Less Wrong, a community consisting largely of above average people in terms of intelligence and ability to follow detailed arguments, is the last place I'd like or expect to see that attitude validated. If your post has substance and says something I didn't know/think before, of course it will take work - apparently even in the thermodynamic sense - to process it...
It's particularly jarring to see a tl;dr appended to posts that took me only a few seconds to read in full anyway.
Or maybe it's just me. I don't know.