Explanation/comparison of differences between ubuntu/kubuntu/xubuntu

Although Ubuntu, Kubunutu, and Xubuntu all say what they are on their respective websites, there is no official explanation of the differences and comparison with screenshots, etc. I just helped out another user who was confused about the difference and i remember being confused myself when i first tried out Ubuntu. Having a page like this could help out new users very much. The closest page we have to this is here http://www.ubuntu.com/products/whatisubuntu/derivatives but it really doesn't offer any good explanation or comparison.