My thing is maximizing my performance: I want the OS to blend into the background and keep as much of my computing horsepower for the applications *I* want to run - not for some stupid transparency-laden theme or other flashy gadgets I don't need.
This is the reason I like what Apple did with OS 10.5: it is actually faster than 10.4 and uses less resources, yet still looks every bit as pretty (if not more so) than Vista. Hmmm.
(Obviously you can disable some of these things to get better performance in all of these OSes, but I think this is just a good rule to go by)
But if you must have Windows (like for gaming): I run
TinyXP on my Mac in another partition for gaming and keep Leopard for everything else
