Microsoft has released service pack 2 for Windows 2003.  There’s a summary of what’s new on this TechNet article, and a full list of updates here.  There’s a marketing promo for installing the service pack, the most interesting points of this release for me are:

• Utility improvements
  Making common tasks easier, SP2 introduces customer-driven improvements to the Domain Controller Diagnostics tool (DCDIAG) and MS Configuration (MSCONFIG) tool. SP2 also has an updated Access Control List (ICACLS) program to allow for greater flexibility when backing up Access Control Lists.
• Management tools made easier
  SP2 includes the Microsoft Management Console 3.0 (MMC 3.0). MMC provides a framework that unifies and simplifies day-to-day system management tasks on Windows by providing common navigation, menus, toolbars, and workflow across diverse tools. MMC tools (called snap-ins) can be used to administer networks, computers, services, applications and other system components. MMC does not perform administrative functions, but hosts a variety of Windows and non-Microsoft snap-ins that do.
• Performance improvements
  Service Pack 2 offers performance improvements for Windows Server 2003 running as a Virtual Server guest under high Advanced Processor Interrupt Controller (APIC) rates. It also improves SQL Server performance under intensive workloads. Both of these improvements lead to more efficient data processing.