Ok, this is not the most useful app out there, but a fun thing to fiddle around with anyway...
Ever wanted to see how you would look if you were a zombie? Get Zombiebooth, take a picture of yourself, and the app will turn you into you. Not just a still photo either, you move around, make zombie sounds and when you touch the screen, your zombie self will start munching on your finger!
Very pretty hey? Shaking the phone generates a different zombie, and you can take a photo with the app itself, or select an existing photo on your phone.
Yup, useless indeed, but fun to show to your friends :)