It seems like the "web 2.0" sites that are making the most waves these days are the ones that have the foresight and openness to release an API and allow users to mash up their content. Google Maps is a good example of this. Although Flickr doesn't really need any help from users to bring it to the forefront of people's minds, they've still released an API. That API lets people do interesting things with their data, and one of those interesting things is Flickr Leech which is interesting in that it was created out of an interest in interestingness. Sorry, I couldn't help myself.

Flickr Leech allows you to choose between Interestingness (by date), By Username, By User ID, Favorites, By Photoset, Group Pool, and Search, and returns a massive set of thumbnails to allow you to very quickly browse your results. Clicking on any thumbnail opens that image's Flickr page in a new background tab or window, allowing you to continue browsing, then view all of the images you selected once they've already loaded. Slick. Probably my favorite part of Flickr Leech is the snarky messages you get on each search - fun stuff.