I've done this in the past but stopped. The problem is there are no atomic transactions in Dropbox. If two people are pushing changes to a repo at the same time using only git, it's not a problem because git understands atomic transactions. But if that repo happens to be in Dropbox all hell can break loose because the various files inside the .git directory are not being synched atomically.

A git repo in Dropbox can appear to work okay with a single contributor where that contributor is only working on one computer at a time. But as soon as you add a second contributor, you very much should take Dropbox out of the process.