For what they are worth,
- Your taskbar shortcut to SW2004 will no longer work (at least mine didn't on multiple installations). Be prepared to delete it and redefine it from the replacement shortcut that the service pack makes on your desktop when you install. Its a bummer, but its life now with the windows installer.
- Be VERY careful about your PWx-2 settings. When I installed Sp1, a couple of unfortunate default settings (which I overwrote in SP0, wishing to get on with things in a useful environment) were replaced again with those unfortunate defaults when I installed the service pack. In particular, the screen gamma correction (which I change to 1 so my screen image correctly previews my render to file) gets changed back to the awful, productivity reducing default of 1.5 (And yes, I lost a bit of time because I set up a rendering assuming that what I previewed on a screen was correct). Also, the default 'scene' that most of us change from the brick background to something appropriate for our industries jumps back to brick when SP1 is installed*
-Ed
*(at least in my experience) I have learned to never make absolute statements here because history proves that things are just quirky. But I SWEAR it happened to me.