User and Blog Pruning

Is it possible to create a plugin which would automatically delete users who are not active in "X" days as well as blogs that haven't had a new post in "X" Days.

Just a suggestion if you are looking for a useful plugin to add to your list. I can see user management as a major issue for me in a year. Short of deleting all the blogs and users every year for the students, I think this would be beneficial to me and the WPMU community.