Like MenthiX said, lots of rumours always fly around about these things, especially when its Microsoft.
This service pack has undergone some of the greatest internal and external testing Microsoft has ever done for a service pack. So I think its good to go. I installed it last night, and have had zero problems so far. The whole process went smoothly.
Some programs need to be updated to work correctly with XP. These tends to be the big programs like anti-virus, but these can be easy to update with patches from the relevant companies.
There is a guide over on
Neowin thats worth checking out for the uxtheme.dll.
