This seems like it would be a dangerous move on Yahoo's part, aside from the acquisition of talent. This is only my gut feeling, but I don't see users being so vested in the FourSquare service, that if they're unhappy with the direction it is taking, just jumping ship to Gowalla. A lot of people already check in through multiple services, and it wouldn't be too hard a decision to stop checking in with one if it's flavor turns sour.