Microsoft announced that they will be terminating their Q&A efforts just as Google Answers did before them. As Ars Technica points out, that leaves Yahoo as the winner. But one has to wonder why they would be ending their Q&A efforts when it seems like Q&A is only getting more popular and mainstream. Witness Stack Overflow as an example, not to mention Aardvark or Hunch as new entrants.
I think the answer is that Q&A is most valuable when it is restricted to a specific community or subject matter. It must have one or the other to succeed. If both are too generalized then you end up with meaningless blather instead of high quality Q&A. That is probably why Hunch is longer term in trouble, Stack Overflow has been and will continue to be successful and Aardvark is ambiguous.
I think the guys at Stack Overflow agree. See video at the end of the RWW post.