I've had exactly this problem too. It would be great to have control over message state so we can essentially mark things for later followup. Simply toggling the read state is one way, or starring them. Whatever it is, needs to be done server side, as I got my GB shipments tangled up by quickly replying to people by iPhone than failing to followup in the right order when back at my desk.
Mhhh, nice matt3o, I didn't know it was possible to create a folder.
I'd really prefer to have the message directly in my inbox and not hidden somewhere else, but hey, that's better than nothing.
It's not following my usual workflow, but I'll try to stick with it for now.