Well, I re-read Brad's article on copyright, trademark and trade dress, and I can see how the examples I mentioned (the Matrix, Xbox, WinXP and OSX skins) actually do fit with the policy mentioned there. But that doesn't mean that I totally agree with it. Specifically, like Koasati, I can't see the justification for the convenient grey area that you allow yourselves.
I am quite willing to admit that I may be one of those who don't fully understand the difference between copyright, trademark and trade dress violations. But I don't think I need to. I can sum up my attitude as: I do not have the right to copy other people's creations. For me that pretty much covers it, no grey areas.
If I recolour the bitmaps in an adni18 skin and post it back here, it's a rip.
If I make an official Spiderman wallpaper into a logon and post it here, it's a rip.
Even if I create a Spiderman wallpaper by drawing the picture myself from scratch, it's a rip. Because Marvel/Sony don't just hold copyright in specific pictures that appear on the Net or in comics or wherever, they hold copyright in the general likeness (the look and feel?) of Spiderman.
Ditto skins based on OS X - even without using the original images, it's still a rip. As Brad says, Apple have brought lawsuits based on trade dress - the look and feel. Put yourself in Apple's shoes - you would want people to make their computer look like OS X by buying a Mac, not by downloading a 100kb bundle of bitmaps to use with a $20 shareware program.
I am just struggling to see how you can allow yourselves this 'grey area' in your policy, where you seem to admit that most of the works are strictly rips, but you will only do something about it if the owner complains. You wouldn't wait for a skinner (who doesn't even stand to lose any money) to complain about a rip - you would pull it as soon as you noticed it, so are you saying that large corporations like Apple and Microsoft are fair game? Or is it because you get a lot of people coming to the site looking for OS X skins, so you are prepared to turn a blind eye

?
Just looking for a consistent approach, that's all...