I actually saw a demo of something like this recently. I can’t for the life of me remember the name, and it was in beta, but it did exactly what you want.
I’m trying to find the link, but so far no dice. I caught it on digg, but haven’t been able to find it again. I’ll keep looking, cause I wanted the damn thing too. I signed up for their mailing list but they haven’t sent anything out yet.
I’m hoping to use it to replace my use of perforce for certain things, simply because a transparent solution would be so much nicer. The only thing I’d be concerned about is security and privacy. But I assume that as they get closer to release, how they address that will become more clear.
Microsoft’s got their relatively new Windows Live Skydrive. 5 GB of storage associated with your Windows Live ID. They provide three grouping for your files - a Private set of folders that only you can access, a Shared set of folders, and a Public set of folders.
I’ve been using it a bit.
Pros: Works pretty smoothly, Free
Cons: 50 MB per file limit, Need to use IE to use their mass file upload tool, Can’t directly move files between online folders