[Rambunctious]

Well, one threat for Google's search business is possibly Apple. By controlling the device, browser and the platform - they have an option to integrate their own search offering instead of relying on third parties. Not sure what the Topsy acquisition was about - but perhaps there is some sort of a social search integration in the works.

And then there's Facebook. The key for them is to figure out a viable business out of head search queries i.e. instead of going after all possible searches. Perhaps mainly target shopping oriented search queries via recommendations from friends?

Of course, this is all easier said than done. Apple has seen its struggles with Maps and even Google couldn't do much with Google+.