I've been on SP2 for quite some time now and have not had any problems execpt one which I knew beforehand:

"As per Christian Dettner's announcement, which sourced from RME. Watch out if you have any Firewire 800 device. The firewire drivers in SP2 will clamp it's speed down to 100Mbps. This affects not just RME but ALL 1394-800MHz speed interfaces."

Couldn't capture anything from my camcoder after installing SP2. Luckily there is a workaround:

"It can be gotten around by restoring the old XP-SP1 version file of c:/wndows/system32/drivers/ohci1394.sys over the top of the new one, after installing the SP2 update."