I’m not a big fan of customized desktop since I regularly clean up my OS every now and then. This is much easier way to spice up the feeling a bit =) Yeah, it’s free.
Also, it has a lot of interesting wallpapers which, of course, are nice. It’s like looking through Flickr with rotating desktop wallpaper, a feature which Microsoft eventually get after Apple has for many years :-P
Check it out @ Personalized Gallery