Enforce a delay between asking and selecting an answer
Some answers seem to be selected within a few minutes of the question being asked. This doesn't always give enough time for the best answer to come out.
At present 1 day seems like a good time to wait for answers before the asker selects the best.
It also makes it easier to remind people to select an answer by popping up when the time has passed.
too discriminatory; we already have problems with people not accepting answers
Sometimes (and I think this will happen more often after the site goes live) the true answer is pretty obvious and appears very quickly after the question is asked. In this case, enforcing a delay between asking and answering pretty much guarantees that the asker will never mark it as answered. I think that it should be left up to the person who asked the question.