I'm not sure about SP3 for XP, since I only uses XP on my laptop, which doesn't see much use. Vista's SP1 that they released publicly was pretty shoddy. I know it's RC1, but still, these flaws were kind of unacceptable.
1. When opening a game, if the computer hasn't been restarted in a while (on for 5 or more hours) It'd just come up with a black screen, but the game was still running. When this happens, you have to either cold shut off, or Alt-F4 a ton of times and hit enter to put it into sleep, then you would get a display again, but you'd have artifacts, so you have to restart anyways. I'm guessing this is a driver problem due to it being a release candidate.
2.Towards the end of using SP1 RC, I couldn't use any USB device that wasn't already installed and plugged in. My friend asked me to hook up his camera so I could upload some pictures to him, I sat there for a half an hour trying to get drivers to work, but they just wouldn't work. So Vista tells me that there is a hotfix for it, but when I try to install it, it says it doesn't apply to my system. I then had to boot up my laptop with XP and use it's card reader. My GH3 controller didn't work either, so I couldn't even get my Frets on Fire fix.
3. While playing back Xvid, it would lock up the computer to the point where a hard shutoff is necessary. The only way to remedy this was to put my processor settings back to stock.
All in all, I was pretty disappointed with SP1, it offered almost no performance gain and gave me a ton of problems. As soon as I uninstalled the service pack, all of the things mentioned above ceased to be a problem.
To top it all off, they justified to me that my $200 dollar purchase of Vista Ultimate was in vain.
http://blogs.zdnet.com/hardware/?p=806 Seriously? Wtf is this? I payed $100 dollars for a black box (which I didn't even: OEM), a poker game and Dreamscene? Thanks Microsoft for giving me Spider Solitaire for free.