If you are still on the fence on the decision to upgrade your Mac to Snow Leopard OS X 10.6, there are now several Snow Leopard Reviews online.
For Engadget it is a clear yes to upgrade, because Snow Leopard is only $29. CNET also chimes in saying that the refined UI and improvements is worth the upgrade. Of course the new Exchange support will find many takers as well.

If you look for speed improvements with Snow Leopard, we reported about initial tests here earlier.

Snow Leopard Review Round-up:
Engadget
Gizmodo
CNET
Walt Mossberg
PC World
Slashgear

You can actually save the time reading the reviews as it is just clear that you should upgrade, unless you are still on a PowerPC. Buy your Snow Leopard on the Apple Store or on Amazon.com.