I also would prefer "Abstract:" to "tl;dr:" just because the latter is, to me, language-aesthetically ugly, and also a bad fit: it's kind of like a strained metaphor that doesn't really add to the message.

Or use the words "abstract", "summary" or "précis", even.

I like "tl;dr" - it gives a refreshing air of disrepute to our site. It's a little like quoting anime fanfiction in that respect.

Yeah, just hurry up and whip out your thesis in its proper organizational context.

Heartily seconded.