Before you get in line tomorrow to get the Snow Leopard upgrade, be sure you have nothing mission critical on your system. It's why I'm still on Tiger on my main workstation. I have so many legacy peripherals and apps that I'm terrified of it all crumbling if I switch. It all works now, and I'd like to keep it that way, thank you very much.
Addendum: From David Pogue's NYT column, I found this link to a list of apps and their current status regarding whether they work or not under Snow Leopard.