Google already knows too much about us.....
I'm thinking they're interested if only for the database of users. Coupled with Google Wallet (ok.. how many use that?), they not only know our habits and what we buy, they know or will know the size of the users bank account. Even more fine tuning on the target.
I am surprised they haven't tried to grab PayPal for the same reason. Right now, they know you go there and probably what you spend. What they don't know is how much money is in the bank.... yet.