Oh, the excitement! I can't wait to get my hands on Mac OS X Leopard. This guide has whetted my appetite; it's 20 minutes long, but it convinced me that the upgrade is worthwhile, just for the new Finder.
If you'll be upgrading this weekend, as I will, do take care and make a complete full system boot-able backup first, just in case something horrible like a power outage happens when you're in the middle of the upgrade.
The trick I used for my system upgrades/moves previously, and with the Leopard beta, was to run an exact copy to a Firewire disk using SuperDuper. SuperDuper is nice because you can at least make an exact copy of your disk that works well in the demo mode.Have fun. :-)