Just want to give you folks some heads-up on the compatibility issues with Windows 2003 Sp1. An e.g. is the problems with installing the Windows 2003 sp1 on a Exchange 2003 Cluster on a Windows 2003 server. More information is provided at the site on how to handle issues such as this.
Here is a list of all compatibility issues with Windows 2003 sp1 and also what is tested and what is not.