Today's the day! As we anticipate Snow Leopard De Prez Allen Laudenslager wants us to know how to do it. He's copied from Daring Firewall an article by John Gruber, "I Believe in Murphy's Law." "How I upgrade to a new version of Mac OS X, from 2007:

So, in short:
1. Do a complete backup clone to an external FireWire drive.
2. Test that the backup is indeed bootable and up to date.
3. Unplug the backup drive.
4. Boot from the installer DVD and perform a default upgrade."

Can you jump from Tiger to Snow Leopard? Read for details and cautions from Wired.
More details are here at Apple Insider.
Note: Your Mac must have an Intel processor in order to run Snow Leopard. See the list of technical specifications from Apple.
Jim Hamm sends some links to articles that will help us check items before installing Snow Leopard. "For example," he says, "is your printer compatible with Snow Leopard?"
From Macworld. From Apple Support. And another from Apple.
Now, whoever is first to put in Snow Leopard, let us know how it went for you. . . Mine was just delivered by FedEx.