Cool idea, similar to what I had in mind using Git's tagging system when I built http://hubnotify.com. Are you using any repo or is the version just in a local database?
Nice site!
Currently tracking the version in a local database and checking for changes hourly via cron. I've half implemented checking github repo's but its not 100% accurate yet. Not sure how you are doing it but I am going to focus on an update being any change to a branch. So its basically tracking branches only.