#git on freenode has some interesting thought about this:

11:44 -gitinfo(jast@infobot.gitrecipes.de)- Storing git repositories on DropBox is a Very Bad Idea™. Use a free hosting service (such as Bitbucket or GitHub), or read !dropbox_why if you insist upon having your repo corrupted.

11:44 <iveqy> !dropbox_why

11:44 -gitinfo(jast@infobot.gitrecipes.de)- git uses a lot of frequently-changed small files, which dropbox's synchronization algorithms barf on. Use of multiple dropbox clients compounds this, with hilarious results