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