> So you need a good solution for resolving inconsistent updates made by two offline clients. The same solution could be used for resolving inconsistent updates made on two database servers.

Exactly what I was trying to get at, thanks. The line between client state, server state and db state is a thin illusion. As REST makes explicit, every client operates on a representation of some server resources, which means CAP can come into play in even the most trivial online apps.