You may be familiar with Woody Leonard. He is a well-known computer book author and Microsoft antagonist. He writes a column for the fabulous Windows Secrets newsletter.
In the latest issue of the newsletter, he referred to the Microsoft Patch Reliablity Ratings that he runs on his web site. His site explains it this way:
I have a rating system that lets individual Microsoft consumers know when it’s safe to install patches. I call it the Microsoft Patch Defense Condition Level, or MS-DEFCON for short. It’s modeled after the US armed forces DEFCON system.
There are lots of patches listed with a description of what some of the problems have been. If you are responsible for more than a couple of computers, or if you are just interested on what is really going on when you patch your system, then you should check out the site.