Service Pack 3 is still fully supported and did nothing to break the system (anymore than it already was). In fact, Service Pack 3 extends the life of XP's support quite a bit. If you're having problems after updating, it's more likely that you simply have a bad hardware configuration. Outside of more well known problems like the .Net Framework conflicts, of course.
I do hate that backported "Windows Search" **** and wouldn't suggest anyone check it while updating.