You should take a look at the topics torrentstorm and i have had on the matter in the past. We usuallt talk about it in an unbais way where only facts about the OS's are presented.
http://rarewarecentral.com/forums/showthread.php?t=3779
Enjoy.
And i'm pretty certain (i'm too lazy to check up) that XP out does 7 in terms of most tasks. Its again (i hate repeating) the security thats different in Vista and 7 as the core has been changed with that in mind + alot of other features and changes but security is the big one.
@TS i agree with everything you said other than the fact that vista is not problematic, its not too bad anymore but when it came out it was screwed.
I have vista at home as well as XP, 7 and Red Hat i don't have any macs but i've used Leopard a bit and played with Snow Leopard. All of those OS's are nice for different things. I prefer 7 to all the others but thats just because it suits my work flow and how i organise work.