You're looking at this the wrong way. Google acquisitions tend to go two ways: talent acquisition, or hitting for homeruns. Is it worth it to Google if they buy a Jaiku and a Dodgeball and a bunch of other relatively small companies and essentially whiff, then knock it out of the park when they buy an Android or a YouTube? Short termers always back, but when you look back over the last five years the overall strategy has been sound.

With specific regards to Foursquare: note that the founder left to do Foursquare, and they're floundering right now. Maybe the vision was never sound to begin with.