I think a saved-games service would be great.
It can be nice way to share saved games and show achievements too, if we would want to do that.
I mentioned that I keep saved games in git.
I have a fair bit of experience with using git for simple file sync and backup.
I use git+ssh for all my code projects, all my websites, client websites, my DNS config, my /etc directories, my important dotfiles, even my mail.
Git is much quicker, safer, and more efficient than IMAP for mail!
Git can compress files much more efficiently than squashfs.
It can keep full history very efficiently, and we can also tell it to forget old history.
I'm setting up git repos for Pandora source code at the moment, and could do a saved games tool / service.
I'm considering to keep a history of unpacked binary PNDs in git, for efficient storage.
I hope to write fusegit, to use git directly as a filesystem.
Not sure it's good for saves, my PCSX save directory takes over 400MB as you need 1-2MB per savestate (even compressed) for something like PSX, I can guess N64 would be similar. Depending on emulator, the savestates are often incompatible with anything on PC, so there is not much point to sync with it in those cases.
I expect they would compress down a lot in git, I'll try it later.
The emulator snapshots might not be portable, but I guess the game's normal save states are?
In any case it's good to have a backup. I'd be angry if I'm 90% through a big game when my SD card catches fire, and no backup! Gaming is serious business!