Tiger > Leopard

Call me late to the game, but I just came across these QuickLook plug-ins that have made Leopard, for me, much less of a lame duck update. The plug-ins for viewing AI files and folders in QL are particularly helpful.

Seriously, aside from the stellarness (of the idea) of Time Machine, what is the big plus to upgrading to Leopard? Similarly, is the jump to CS4 from CS3 worth plunking down its Voyager Spacecraft-like sticker price?