> What USB needs is a real transactional file transfer class, think of FTP over USB.
I was thinking more along the lines of SMB/CIFS over USB (with optional UNIX extensions), but the principle is the same. Take a decent network filesystem protocol, adapt it for point-to-point use over a single, arbitrary, byte-oriented channel, standardize users, groups, and permissions, and then layer it over USB.
One nice thing about using SMB/CIFS would be that it could be implemented for most current operating systems with a simple USB-to-IP proxy and existing network filesystem drivers.
FTP (or WebDAV) would probably work just as well; I'm just not sure about potential protocol limitations. I've never known anyone to use FTP as a network filesystem protocol.