Interestingly enough, you should not attempt to install new operating systems on machines that have faulty logic boards. I began to realize this after my Leopard install failed about five or six times.
As a bit of backstory: a few months ago my MyBook died (theoretically), which led me on a crazy chase to figure out what the heck was going on with my Macs and hard drives. The second and third hard drive replacements worked over USB but not Firewire. Long story short, it seems that some cheap Western Digital Firewire cables fried the Firewire on my iMac, my MacBook, and the drive itself. Three replacement hard drives later I found this out, and promptly got my MacBook's logic board replaced to fix the Firewire ports. My iMac is currently in the shop getting the same treatment.
Unfortunately, it seems I got a faulty logic board for my MacBook as a replacement. Firewire ports work now, but two or three times a day it just powers down... no errors, no logs, nadda.
Naturally, an OS update would be prime time for those shutdowns to occur. So that happened a good five or six times until the one happily went through without a hitch, which brings me to the present: typing on a new Leopard install.
It feels good, too.