MS has released a patch that prevents people form upgrading to SP2 unless they remove a spyware program that has been known to restart SP2 computers. It only happens on Windows Update, so if you're planning to upgrade in a way oter than WU, then you should probably run AD-Aware and Spybot S&D.

Full Article:
http://www.pcworld.com/news/article/0,aid,118172,pg,1,RSS,RSS,00.asp