The new SDK now has two versions. One for Leopard and one for Snow Leopard.

Some info on the new SDK:
-Requires OS X 10.5.7 or Snow Leopad Final Developer Preview (Build 10A380)
-You can now use the iPhone SDK 3.0 for submitting for iPhone 2.2.1 applications

File Sizes:
-iPhone / iPhone 3G / iPod Touch G1 : ~230MB
-iPod Touch 2G : 258MB
-SDK for Leopard : 2.1GB
-SDK for Snow Leopard (get this) : 404MB !?!

Just went through the release and not much has changed feature wise from beta 5. I'm not telling! Not sure when beta 5 is going to expire but I upgraded all the devices just in case.