I just posted a blog on a little known feature that is pretty cool. I thought it was neat - I figured it has a lot of uses, so why not point it out to people in case they find it can help them:

http://management-platform.blogspot.com/2012/03/monitoring-custom-data-from-...

Its essentially a way to collect metric data from simple SQL queries. But because its a "normal" metric, you can track it historically over time on the graph view, you can alert on, etc.