I've seen a bunch of #3 going on here in the Israeli startup space, but I hate to admit that I can't think of any names right now.
Oh, except face.com. The requirements of face.com's face recognition, and the fact that it's searching bazzillions of photos on (also cloud-based) social networking sites, means that they are built specifically to live in the cloud.
I'm sleepy or else I'm sure I could think of some other names. ummmmm... *shrug* I'll come back later when my brain is working, k?