Personally, I'll be (very) happy if the wallpapers there are all watermark free, it will save me the time to discard the watermarked ones...
I see watermarked wallpapers a bit like a curse, ruining my perfect image with that thing. I don't mean that it's wrong to put a watermark, just that it feels like that in my eyes, making me discard the image.
And I've the sensation we'll see enough non-watermarked wallpapers anyway.. ^^

A very nice website for wallpapers is also: www.socwall.com
of course, these images all need adaptation in dimensions.

To the webmaster: is it possible to add a voting system? just like "+1" and "-1" under the image? (as in the website I just linked)