“First, thanks to all of you that took the time to describe the different problems you encountered. You know who you are. Second, do not see this as an attempt to knock SP4 and tell you to not deploy it. This SP has hundreds of important security fixes, so it is important. The main thing I am emphasizing is that you need to TEST, TEST, and TEST in a non-production environment FIRST.“
Here is a nice summary of problems encountered by some users with SP4. In addition to these potential problems, I had a problem with my zip drive.