Good question. With my understanding, being that Greplin has access to all private information, they have an incredible amount of power -- in fact more than Google who just has one/two aspect(s) (albeit large ones). Just for the sake of privacy, imagine Greplin agreeing to giving up private user information to the gov't, just like all these other companies? They'd have access to everything.

Scares me a bit too much to sign up for the convenience.