Wow, new wallpaper is the best feature of a new OS, even though that wallpaper can be installed in any other operating system that exists? Genius. Furthermore, those wallpapers are indeed ugly. In fact, I don't like any of the built-in themes Windows 7 currently has.
I like cool wallpaper as much as the next guy, but as stunning as many of the wallpaper options have been in Windows Vista/7, most of them are unusable. Why, you ask? BECAUSE I CAN'T SEE MY ICONS. I refuse to use wallpaper that is so blinding that I have a hard time finding icons on the desktop because of it. It's not that I can't find them, but it shouldn't have to be a chore to do.
I generally find images that have enough darker color around the outer edges so I have places to put the icons where one can easily see them. Microsoft needs to drop Apple's form-over-function mentality with this stuff and actually give us themes that not only look good, but are reasonably functional as well, and finding usable wallpaper is as good a place as any to start.