On a Linux (Ubuntu, although a non-distribution-specific solution is preferred) machine, I would like to give another user read and write access to some of my files. Neither of us is an admin, so we can't create a group. Can this be done?
Check if there is a "getfacl" command.
If there is such command you are able to use ACL's. It is extension of standard privilages system. You are able then to run command:
Other than to rsync back and forth, I cannot think of a "good" solution. I'd recommend something like this:
Therefore you always have your copy. After that I'd "diff out" the files changed.
I wouldn't recommend giving immediate write permissions; I can imagine some file-locking issues.
I'd suggest a common NFS/FTP share somewhere else.