6 Companies Google Should Buy Right Now

Valve: This makes the least sense to me. You shouldn't enter a highly competitive market (like games) as a side project.

Twitter: I don't think all that many people care about the real time web. But even if they did the question becomes "Why couldn't Google create a search engine that crawls Twitter every few minutes?" They don't need to own Twitter to make a real time search product from Twitter's data (which is all public after all)

StumbleUpon, Last.fm & FriendFeed: In all these cases the author assumes there's some value in knowing what the users of these services find interesting. But the truth about all of them is they have a very small niche audience. Meaning if Google used them they'd be skewing their results to a small audience while possibly alientating everyone else.

Of course if a site is a sensation and has an established community in a short time that may be worth purchasing but overall I don't think we'll see Google going after any of these.