I guess, or rather I hope that when we see Snow Leopard ALL....lets say Core Duo, Core 2 Duo etc notebooks and systems will see a significate performance boost.
I agree that Tiger is a little snappier, probably because Leopard is Tiger but with a load new features.
SL should be more refined and thus quicker with its new 'Grand Central' -
Multicore
“Grand Central”, a new set of technologies built into Snow Leopard, brings unrivaled support for multicore systems to Mac OS X. More cores, not faster clock speeds, drive performance increases in today’s processors. Grand Central takes full advantage by making all of Mac OS X multicore aware and optimising it for allocating tasks across multiple cores and processors. Grand Central also makes it much easier for developers to create programs that squeeze every last drop of power from multicore systems.
As EVH will agree, our Mac Pro's were actually more than the software could handle or utilize.