Oh zipperman
SP3 includes all the updates since SP2 (this part we all agree on, I hope)
But since SP3 release (now been a short while) there have been
more security updates !! On top of SP3 (another good reason to get it actually)
Anyway, many users elect not to install SP3 (even support members sadly)
Everyone should realize that it's not really a personal choice thing. They are Security Updates, if you don't get them, you'll be
not secured against potential attacks on your (well MS) Windows Xp version.
In some instances (all of resolved
fully now by MS) some users reported SP3 created more havoc. Thankfully for this reason both Add/Remove Programs and System Restore can be used to uninstall it. But. These problem installs are actually to do with your computer makeup, not SP3.