but it did happen to me and i'm not exactly a novice.
obviously Your Mileage May Vary. i was just recommending caution.
i could have upgraded to SP2 i've done that a many times on various computers with no probs since some online software simply won't install on SP1.
i just don't know of the marginal utility that SP3 brings.
i don't think people should be scared; just have backups and utilities handy (as most major upgrades recommend) in case the unforeseen happens.
And in my case my PC is a SFF unit that was very hard to fix after the fact
SP3 does run quite nicely on my PC after the the Video and Audio drivers were reinstalled