How are any of these proposed mergers actually going to, y'know, work? As far as I can see, the only compatible culture for Yahoo is Google, and anything else is going to mean a huge exodus. Of course, with all of the ex-googlers roaming around SV, a few thousand more from Yahoo could make for a very interesting startup climate!
huge exodus is not the end of the world for microsoft... they get the traffic and products, and the work force has reduced itself for them with no need to pay severance or benefits.
actually, exodus from yahoo might be good for ms+yahoo (no severance etc.) and for google too (good talent) and ofcourse as you mention, nice startup environ.