There's one single thing on SO, I really hate: The limitation of "allowed questions". I really don't see what's wrong with "questions having no answer", "too argumentative", etc. For sure, not everybody is interested in such questions, but there always question, I'm not interested in, no matter how many search criteria I use. I consider closing such questions or moving them really strange.
Something like the tag "normal question" could filter them out, while they'd stay more easily accessible for those who are interested. There are also questions on the edge (sometimes I'd ask something like "Do I really need to it that complicated in Java, is there a better language for this?" which could be answered by "there's a simple solution" or "language XXX is much better in this respect". I really see no reason why I should log in into multiple sites when I'm interested in different aspects of one thing.
Don't get me wrong, I actually find SO fantastic, I'm quite new here, but I see the unbelievable speed and quality of answers, the really nice editing and formatting, everything is much better than I've seen anywhere else.