"I saw a simple Java question, hit Google, read briefly, then
synthesized an original answer."
1. To ask interesting questions that I think will get a better answer there than anywhere else (eg [0,1,2]).
2. To help educate other programmers about languages that I like very much, and would like to see in wider use. I endeavour not to just give a "how to do X" answer, but instead explain what the different approaches are, and why some approaches are better than others (eg [3,4,5])
3. To stay in touch and build a reputation among the wider community of Haskell programmers - not by amassing internet points, but by asking interesting questions and giving interesting, thoughtful answers.
If you just game Stack Overflow for imaginary internet points, it's no wonder you don't find it very fulfilling.
[0] http://stackoverflow.com/questions/9190352/abusing-the-algeb...
[1] http://stackoverflow.com/questions/10753073/whats-the-theore...
[2] http://stackoverflow.com/questions/19177125/sets-functors-an...
[3] http://stackoverflow.com/questions/11684321/how-to-play-with...
[4] http://stackoverflow.com/questions/12968351/monad-transforme...
[5] http://stackoverflow.com/questions/20857165/move-or-copy-in-...