Its allows you to ask a question and then bring it to the attention of everyone who likes a certain topic and your friends of course. Then those interested in the matter can respond to the thread.
I dont find it unlikely that this will become popular and will start to rival forums, because it addresses / invites people interested in answering the questions. Much different to Yahoo answers. And its reach is very large, so it may well be able to focus large number of people that would otherwise turn to niche forums.