I had some bad initial experiences with SP2. I tried slipstreaming it with my Dell Windows reinstall disc, but it kept screwing it up. Probably just unique to my Dell OEM disc.
Now I'm running XP Pro with SP2 slipstreamed and my 'puter is running 50 to 70 percent faster than ever before.

The biggest thing is some rewritten core code I think, aside from all the security fixes.