Today, the guys at PerfectDisk announced on their blog that a new build of PerfectDisk 2008 for Windows Home Server is now available. This new version includes full integration with the Windows Home Server console, where PerfectDisk 2008 will now have its own tab.
The PerfectDisk software defrags and optimizes disks which leads to better performance and reliability. Their "Space Restoration Technology" also helps create a large piece of contiguous free space so there is less fragmentation in the future while also improving write file access, whereas typical defragmenters only focus on read file access.
If you already have PerfectDisk installed on your WHS, you'll need to remove that first before installing the latest version. Installation instructions are here. The software for WHS is only $39.99, or you can purchase a Home Site License and get 10 licenses for your network for $99.99.