Windows XP SP2 Impressions
A roundup of concerns and problems with Windows XP SP2 from the early adopters: Many, many users are reporting problems with SP2 limiting outbound TCP/IP connections. This appears to be nailing anyone who makes heavy network use of their machine, including especially users running P2P applications. A Microsoft blog rounds up some reports, as does SANS. Microsoft has objected to people helping them distribute SP2.
Control Panel -> Add/Remove Programs -> Windows Components -> Networking Services -> Peer-to-Peer "Enable Peer-to-Peer Networking Services."