If you are expecting big things from windows XP SP3 and curiously waiting for it then its better you do a reality check. Hope my study in that direction would help you.
As we all know, Microsoft windows service packs are the one shot installation set which includes previously released all security updates, hot fixes, stability and performance updates and SP3 is such a package with a small number of enhancements which do not change the user experience but it fills the gap in the updates we might have missed by declining individual updates when using windows updates or during custom update installation.
One thing is pretty much clear that SP3 will not bring any outstanding changes or enhancements except adding one new feature that is Network Access Protection, borrowed from Windows Server 2008 Technology and the rest will be the updates/hot fixes/patches covering from the era of Windows XP SP1 and SP2.
The Windows XP SP3 Release Candidate is available for download. Microsoft cautioned this is only for testers and not for primary or mission critical systems. Here is the URL http://www.microsoft.com/downloads/details.aspx?FamilyId=75ED934C-8423-4386-AD98-36B124A720AA&displaylang=en
There were rumors floating around that SP3 may come up with many new functionalities borrowing from Vista and 2008 Server technologies, but the question is why would Microsoft is going to do that when it already released its newest versions of operating systems (Vista and Windows Server 2008)? How fair it could be, we expecting new features to be included in SP3 rather migrating to latest operating system (Vista) which Microsoft will sure push with more pressure in near future. But the other side of the coin is, Windows XP proved as a most stable and reliable operating system and industries are still showing interest on continuing with it rather migrating to Vista which strongly recommends few hardware upgrades.
The SP3 documentation clearly states that “Microsoft is not adding new features or functionality from newer versions of Windows to Windows XP through SP3”. If you have downloaded/applied windows updates till date then SP3 may not bring you any big difference.