That's a nice one. Didn't think about that. It's a nice compromise between client and server solutions.
Store-and-forward has another big set of issues though. File sizes and bandwidth requirements are easily non-trivial. In addition, there could be legal issues with keeping the data around for awhile and then forwarding that wouldn't exist if you just piggy-backed on some other app. In a way, it kind of puts you in the league with GMail and the other guys, right?