One good reason to consider an upgrade to Vista, Microsoft’s just-released upgrade to Windows: the default set of desktop wallpapers it ships with include several from Flickr members. Long Zheng has a blog post with some examples, and Microsoft’s Raymond Chen has more details.
Reportedly, Microsoft experience designer Jenny Lam considered around 10,000 images, combing traditional sources and commissioning a few photoshoots, but is happiest with the ones that came from Flickr members, like these from Hamad Darwish AKA [ HD ]: