Christophe-Marie Duquesne has just announced Sharebox, a FUSE filesystem relying on git-annex:
What are your goals? Seamless synchronization "à la dropbox". Ability to use with big binary files such as mp3/movies. Entirely decentralized. Don't use unnecessary space Keep it simple: avoid special VCS commands and keep a filesystem interface as much as possible.
While still alpha, this is promising. --Joey