A major problem has also been on some HP/Compaq Media Centers with AMD processors... blue screen of death, reboot, repeat.... safe mode attempts hang before safe mode loads... I would hate to be a non-literate computer user and wake up to this and have no idea what to do. There is finally a fix for this but it should be installed first, and it is an HP patch, not something that MS updates would push.
Other than that, I've only seen minor problems with SP3, and I've literally installed it hundreds of times in the last couple months since it came out. It certainly is not something they should push with Automatic Updates.... idiots!... wait, did I say that, I am a MS partner...I didn't mean idiots... I Love Microsoft *smile* $$$$$$$$$$$$$