You might want to take a look at Coda instead of NFS. It supports "disconnected" read/write: http://en.wikipedia.org/wiki/Coda_(file_system)I haven't used it though.
Hey thanks! This seems quite cool! I've read about it on their website also and it would clearly fit all my "requirements" for a network FS. I believe it could even be used to replace completely my current use of unison.
Definitely worth experimenting and if that succeeds, I'll consider migrating to it! Thanks again! Simon