Sorry I don't have a link, but I remember reading that while it is wonderful to be acquired by Google, it was a considerable challenge to make your product run on Google's infrastructure. How many times have we seen a product change dramatically or be shut down after acquisition by Google? Writely, JotSpot, Dodgeball, and Jaiku come to mind. Android eventually became something very important. In acquiring, Google gets talent, publicity, and code.
Dodgeball ended up becoming Latitude didn't it? It seems most products are really transformed post-acquisition (which is probably hard on the founders)
I imagine infrastructure and code can rarely be reused from company to company, so I'm not quite sure what Google gets out of the acquisitions.