Hmm. And what should we do with the players that complain they mixed up the save with the server and now they played x hours but cannot use, what they built. 8-) This could be completely transparent to the player since it would appear to them to work in exactly the same way as it does now for multi...

I have often thought that it would be useful to have multiplayer map downloads use something like rsync, which can compare the files and download only the differences. It's not an issue for small maps, but if you have a large save file with several people playing then it can take quite a while.