Google would only acquire Yahoo, should Yahoo be just about to disappear - if that's even possible - or if it was going down fast. Only than it would justify to take over the patents and staff at a fair price, without paying extra for the "junk" which is supposedly sinking.

However, on the other hand Facebook would do just fine if they acquire Yahoo. As soon as Facebook's stocks get more stable and the fuss settles, I'm guessing Dec/2012 to Feb/2013, Facebook's shares will be going for a "very fair" USD15 ~ USD21. But if they launch their mobile device in that period, then I guess their shares will rock on USD25 ~ USD31 Anyways, considering the mobile device is not arriving before Q2 2013, then without growth and new features and afraid of new comers, the board will realise than they need content and loads of patents if they are to take on Google's array of products. And Yahoo will fit Facebook just like a glove.

However, Microsoft fearing for it's lack of social presence and weak search-engine, will possibly start a bidding war. Cutting the story short, I'd bet Facebook takes over if not completely, at least a good chunk of Yahoo, by the end of 2013.