There have been several issues with applying Windows 2003 Service Pack 1 reported on the newsgroups varying from Crystal Reports not starting to getting HTTP 500 errors.
We are therefore advising our customers not to install W2K3 SP1 until we know what the issues are and how to fix/avoid them. Will update with more information as we find out.
On a further note if you have SBS2003 (if you read some of my older posts you will realise what a fan of SBS I am) then do not install the Windows 2003 SP1 – there is a separate Service Pack 1 especially for SBS2003. The SBS Diva has all the information you need for SBS2003 SP1 but again if you have CRM on your SBS server hold off for now.