Thanks for sharing, I'd never heard of git-notes before! That's really cool. I'd previously wondered why there wasn't something like this available; it looks like I just wasn't aware of its existence. I definitely agree that you could implement many powerful features using this.

Now I'm wondering if someone has implement a release tracker using git-notes. After you tag the release you could build / generate the output assets (e.g. binaries), upload them to some remotes (e.g. S3, GitHub, your server), and add a note with the release info plus some links.

I've already thought up a couple ideas for things that could be built on top of git-notes.