So, How Much Should I Trust Microsoft?

My computer just downloaded the new Widows XP Service Package 2, and it wants to know whether it should install the thing. Frankly, I'm not sure what to tell it. I mean, I've heard some horror stories. Any of you Loyal Readers know anything about this at all? Specifically, does the Home Edition of XP tend to have problems with the new package, or is it just the Pro version? And, if I already have a firewall set up (which I do), do I even need to install SP2? I took a look at Microsoft's website, but it's never terribly helpful...