I have used it since it was an RC. Its makes it run a little smoother and makes sure you have all the updates you might have missed. If you are using WMP10 and don't want to up grade to WMP11 make sure you uncheck the box. Same goes for IE6 and IE7. You can always uninstall them in Add & Remove Programs and they will revert back. SP3 is more of a benefit than a bad thing!