I recently received correspondence from a fellow Mac consultant who had a very bad experience using the disk defragmentation function in Drive Genius 2 from Prosoft Engineering. His Leopard setup on his MacBook Pro was completely hosed after he ran disk defrag. He then turned to Disk Warrior to try to repair his computer. After running for 4 hours, Disk Warrior had found 697 overlapped files and had still not completed. Using Time Machine, my colleague was able to recover all of his data and programs except for a few documents that had changed since his last backup.