Actually, Snow Leopard is slightly more than just a partial upgrade or service pack... yes, I get that the overall functionality appears the same but there is quite a difference now that Apple has brought ALL of their applications to 64 bit... so Apple Mail (with included Exchange support - something Microsoft charges quite bit extra to get even on the Windows os), Safari, Core Imaging, Garage Band, and on and on are all 64 bit. Well worth the $29.
And as far as pertains to this thread, the good news is that it looks like all Adobe apps for the Mac in CS5 will get 64 Bit Cocoa makeover and drop the antiquated Carbon. I can say that Dreamweaver, Fireworks, and Photoshop have all picked up noticeable speed and stability even as 32 bit apps on Snow Leopard - can't wait for CS5 with 64 bit support.
Cheers,
Brian