Giving them my entire life (a lot of what Google has + a lot of what Facebook has + a lot of what Twitter has + a lot of my files if I decide to do Dropbox) raises serious privacy concerns. But it looks so awesome that I don't give a damn.

EDIT: But I am refraining from doing GMail, Google Voice, or Dropbox for now at least. I try not to do any communication that I truly care about staying private via Facebook or Twitter, so those don't concern me as much.