Update: the service described in this post is no longer available.
Any University of Michigan engineering student is familiar with the process of finding an open CAEN (UM's engineering computer network) computer in the library or other engineering buildings - you walk around for 5 or 10 minutes until you find one.
After using that process a few hundred times, I finally got annoyed enough to do something about it. I skipped a Theory of Computation recitation one afternoon to implement an email/SMS interface which one can use to check the utilization of all CAEN labs in a building.
CAEN provides realtime computer status here. The HTML is kind of ugly and scraping it was messy; my scraper uses a combination of HTML Tidy and PHP's DOM/XPath functionality. My service pulls an updated status from CAEN every two minutes.