This is the cutest Twitter App: http://neco.tter.jp/

It's like tamagotchi kitty meets Twitter. You sign up for a cat (that's neco in japanese) and neco.tter.jp creates a twitter account for that cat. When the cat says it wants food, or talks to you, or poos (oh so japanese!) you @catsname with food or cleaning or just talk to it. On the website they have a kitty ranking page so you can see who's getting the best care: http://neco.tter.jp/necos/ranking