Are there any ready to use file system implementations available?
I've personally only used SSHFS (years ago). It was ok - slightly flakey for me. I can't remember what was wonky, but it was like 98% working, I couldn't figure out the last bit, so I just switched to straight up SMB/samba (I had pretty free control of the remote end, so that was a reasonable solution).
Maybe I'll give SSHFS another try again now...
SMB tunneled over SSH works better in many cases, but of course that has it's own set of problems and is a huge pain to set up.