As the resident "I want my commits to be beautiful" purist around here, I have to say that I really, really dislike this idea. Commits are rarely exactly bound to a specific billable item on an invoice.

Implementing a feature could and often does cause mutliple commits.

A system like this either encourages to mush everything together into one commit (bad) or it creates basically empty or non-related commits after implementing the feature so it appears on the invoice.

But this is just me. I see how this could be useful for people who are not such purists as I am. On the other hand: In my SVN times, I would have used a service like this in a heartbeat. Even in my early git days.

But after learning about optimizing commits and about the beauty of a clean history, I now changed my mind about this. So ask yourself: Is there any chance you might shift in your thinking about the commit history? If yes, do you really want to have commits in your history that you might at one day consider to be really bad ones?