Calling it game-changing is (to me) a little hyperbolic. It looks to be convenient and time-saving, but my search problems extend primarily to Gmail, which already has great search. To each their own, but I very infrequently use FB/Twitter search. I actually sort of distrust FB/Twitter search (e.g., search is not finding something I'm positive is in there), and adding an abstraction layer doesn't alleviate any of that distrust.
To be completely honest, if Greplin were acquired by Google or MS, I'd be more willing to try their service out. I understand that they're using authentication mechanisms that don't require credential caching, but my content is on there somewhere. This is more of a touchy-feely paranoia thing, and not exactly backed up by any technical facts (i.e., for all I know, the smartphone in my hand has malware on it that is broadcasting my every keystroke to some teenager in Russia, so worrying about greplin may not make a lot of sense. But I can choose to use/not use greplin, whereas I'm sort of stuck with my phone).
Again, this is the value-proposition to me. I don't generate/consume enough content that I need cross-site search at my fingertips. I would imagine that others who are more involved with social sites would appreciate a tool like greplin.
But somehow they need access to my data, right? To index it?
So we're working on the promise that they won't do anything dumb or evil in the future. Not with that index, nor with the API tokens that grant them access to, uh, all my online data.
Great for people who have always wondered "Why do I need so many stupid passwords, I have no secret data anyways" I guess.
From the article: "Greplin only uses OAuth and other APIs for authorization, so they never see your third party site credentials".