I found this article informative. I didn’t actually know the details of how the credit score is determined. But I especially found interesting the conclusion that Uncle Sam is (or should be) a sub-prime borrower.

Update (January, 2014). I’ve been asked to remove the link because it’s causing the originator’s spam rating to go up. Sounds like a bug in the algorithm. Here’s the equivalent link, in case it’s helpful: http://goo.gl/swFwgW.