I like the idea, definitely need a Windows client though. I think you should also release pricing pretty soon, I don't want to go through the effort of uploading photos if its going to be very expensive all of a sudden. I'd also like to point out that 'a few gigs' is not very many photos these days. I'm not photographer but I had 3-4 gigs of photos after my recent 3 week trip to the USA on just a fairly basic digital camera.

Your price point is going to be a tricky one to pick. Dropbox charges around $10 for 50gb, which if I was only using it for photo backups, would be too much, and I'd not do it.