Microsoft has released a white paper on Windows XP SP3, which can be downloaded from the Microsoft download center.
Windows XP Service Pack 3 Overview
Although at present XP SP3 is in RC1 stage and is available only at Connect and was also recently made available to TechNet/MSDN subscribers, this white paper has been released. This will be very useful for those who wants to deploy this service pack.
This white paper summarizes what's new in this service pack.
I have installed SP3 RC1 and haven't faced any problem.