I consult clients at their home or office using my dual-boot PowerBook G4. Until today, my laptop had been configured with separate Tiger (OS X 10.4) and Panther (10.3) partitions. This morning I reformatted the Panther partition and replaced that operating system with a clean install of Leopard (10.5). I then ran Software Update to install the current versions of iTunes and QuickTime. I chose not to install and test third party applications in Leopard. Instead, I decided to run Verify Disk and Repair Disk Permissions in Disk Utility as part of my normal OS upgrade procedure. While Verify Disk finished without a hitch, Repair Disk Permissions crashed and locked up my computer. During the afternoon, I helped a customer complete the setup of his new iMac which was configured with Leopard. I ran Disk Utility on his Intel iMac which froze during the Repair Disk Permissions process.
Moral: Stay away from using Repair Disk Permission in the Leopard version of Disk Utility until a bug fix is released.