If it works on your machine (and the only complaints I've heard are WRT various drivers and some AMD laptop issues), it is the most solid Windows release I've seen.

As far as I'm concerned, WinXP is all I'm ever going to need from Windows, and SP2 or later really cleans up quite a bit of cruft. SP3 actually improved kernel dispatch speeds in WinXP; I don't know whether you'd notice the speed increase in typical applications. SP3 also added some security features from Vista, but leaves the user interface alone.

http://www.windowsecurity.com/articles/Windows-XP-SP3-Security.html