Leopard ran "snappier" than Tiger on my MDD. Just like every other iteration of OS X (more recent = faster).I'm sorry to disagree with the others, but unless you use the new features in Leopard (which I still don't), what's the point of making things slower? Tiger - in my opinion - is by far, the most stable and efficient OS that you can have on that machine.
No Spaces and Time Machine, but do you really need them? I wish SL would be more like Tiger!