Would have expected Microsoft to buy newsgator as they do integrate into Sharepoint. Yammer IMHO is an island where integration in SP is low. Then take into account that a lot of yammer users have a free account but hardly use it as there is no user adoption program and we know that that is important to get everybody involved and not just the more experimental people. Third why pay $1B for an activity stream?? For that money MS could make their own. Not that hard to implement an (almost) open standard? We ll see if the rumor is right and see if yammer will be integrated into Office like Skype and Groove.