Zeffii's question comes close to, but is a little different from, something I've been thinking of for a while. The scenario is that a user, who may have only come to the community to ask one particular question, asks that question—a really really good question—and gets a really good answer. And having gotten the answer, leaves the community before accepting the answer. The reasons for non-acceptance are not as important in this discussion as the fact that it did not get accepted. And because it never got accepted, it has remained marooned on the unanswered questions list.
A similar situation would be where after a question was asked, and an answer was accepted, a much better answer was offered--more thoroughly complete, better resourced, &c.
Should there be some mechanism by which the community, or the moderators operating on the community's behalf, could accept answers, or mark a different answer accepted than the answer originally accepted by the original query poster? A parallel to the "close" vote comes to mind as a reasonable parallel.
Or is this question worth moving up to the "Big Meta" discussion list?