Nmap Hackers: Windows XP SP2: Nmap Fix and Further Information contains a useful explanation from the author and a clearly marked rant.
Fyodor has released a version of NMAP that provides a workaround for the fact that Microsoft has removed access to RAW tcp sockets in XP Service Pack 2. He's also given a critique of Microsoft's policy which has effectively broken the useful systems and network administration software he wrote, NMAP. One of the footnotes led me to a detailed explaination of the changes posted on the Microsoft site. As I read over the list of changes at Microsoft it occurs to me that the same people who have problems with their computing networks because of misconfigured host based firewalls will probably be more than a little affected by the changes to Microsoft's strategy here.
I think that well configured and maintained XP machines in small business networks will benefit from some of the features in SP2. If you support XP hosts, be prepared for problems, and plan to spend time dealing with these issues over the next few months.