Antivirus software screws up a lot of installs. In fact, it's commonplace to disable antivirus stuff before starting a major upgrade (at least if it's something you can't easily uninstall and reinstall). I can't believe an IT proffessional didn't realize that.
I know I've installed games that didn't run on the first install because of my antivirus stuff. I highly doubt that is Microsoft's fault.
SP3 runs like a charm; in fact speed tests show it runs up to 33% faster than sp2. I don't see any giant, "BUY VISTA" advertisements and every single program that ran on SP2 runs exactly the same as SP3, except faster.
!Oh and one more thing. Removing a Service Patch can be highly risky and may in fact force you into a full windows reinstall or format. If you have problems thats one thing, if you are paranoid about MS manipulating you into buying Vista, well, I've got good news! XPSP3 is still way better than Vista even if it was just a giant trick and it put in some invisible bugs that have no effect on anything.