Perhaps as a certified Old Grouch(tm) I'm merely being paranoid in that I use a three step approach to this problem: 1. local project; 2. backup project to thumb drive; and 3. backup project to the cloud. Of course there is a reverse approach to synchronize accordingly. I also would like to see some attention paid to the traditional problem of "Who's on first" that invariably arises when number of participants is greater than 1...
No, the name of the player on 1st is named Who?
I'm sure git would work for most people. A more UI / user friendly version of git with cloud storage support for like.. a photography firm workflow? would be interesting.
Not quite geared toward photography, but your description reminded me of http://layervault.com .