I get frustrated when I see a question that I can answer, but the question has been already been answered wrongly by somebody else, and that wrong answer has been accepted. Usually this has all happened within a day of the question being posted. Many questioners seem to immediately accept the first answer they get, which encourages fast-but-sloppy answers over right ones.
My proposed solution is to prevent any answer from being accepted until either (a) several days have passed, (b) several answers (from different users!) have been posted, or (c) a single answer has received a number of up-votes.