Yes and we can find tons of examples where they haven't done well, e.g. Jaiku which they pretty much threw away, Dodgeball which let the founders leave in anger and got them to found Foursquare outside of Google etc...
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.
