Hmmm... Me thinks I will hold off for now. Me has better things to do than fool around with a major OS upgrade...
Was your first attempt a basic upgrade or did you do an Archive and Install?
I did do an archive and install, and performance was flaky in 10.5 and 10.5.1, and totally useless in 10.5.2. I still had Applecare and they suggested I stay at 10.5.1, which I thought was ridiculous. I Googled "leopard upgrade finder crash iMac G5" and found a post where the user did a clean install and migration from a backup disc. I had a solid 10.4.11 backup and this worked. I do have the APE pref pane disabled as the Leopard Insanity haxies brought back the finder crash. When the finder loads, no apps or discs appear on the desktop- although you can launch apps from the dock. My daughter had no issues at all upgrading on her MacBook that had shipped with Tiger, but that's an Intel processor.