Microsoft released Service Pack 2 for Internet Security and Accelerator Server 2004 on February 1st. You'll want to go hereand check out the release notes and download it right away if you're using it.

There's also a white paper that goes into great detail on the changes and enhancements in this release. If you're evaluating Windows Server R2 you'll especially want to get this service pack as it contains support for R2.

Found on Bart De Smet's B# blog.