There are at least two old threads discussing Windows 2000 SP4, but I didn't want to open up an old one with new information. For those of you who are hesitant to deploy the service pack because you want the bugs to be worked out first, there is a web site set up which lists all of the known issues with SP4, and, as far as I can tell, it gets updated when new issues are resolved. The link to the site is below. Maybe it'll help some of you decide whether you should deploy the service pack now, or wait until some of these issues are resolved.
Windows 2000 SP4 Issues