By now you are aware that SP2 is out for Windows Server 2003 and R2. I have already seen quite a few posts in the public newsgroups where people are not aware of a few things.
It is a really good idea to backup your system before you attempt any major update or service pack. Remember your backup is only as good as your restore. Or as Geoff N. Hiten SQL MVP and SQL God says “Until you test a backup by restoring, you don’t have recovery plan, you have a recovery hope.”
Another good idea, read the readme or release notes. They can be found here Release Notes for Microsoft Windows Server 2003 Service Pack 2.
Next and maybe most important is to check with your hardware vendor before installing. They might not support it yet. For instance Dell says they don’t have any reported issues, but EMC (A Dell partner) does not support it yet.
You will have to take an outage to install this on your cluster. Please read How to install service packs in a cluster. Please note that this document has not been updated for SP2 yet. I won’t bring up the mess everyone had to deal with on Dell’s for SP1 (see http://www.dell.com/downloads/global/power/ps2q05-20050113-Callaway.pdf or better yet http://msmvps.com/blogs/clustering/archive/2005/06/28/56167.aspx).
I remember growing up as a kid and going to Circus World and getting a small usually square white box with question marks all over it. They sold these for $1.49 – $2.99. The more you paid, the better the crap they put in. Installing Service Packs from just about any vendor is exactly like this. You really never know what they have changed, thrown in, made better or worse.
Always test a service pack install on a test cluster. Bad things happen when you test with production servers.
Good luck and keep me posted on your experiences.