I love the idea of an app that can take my mediocre skill and turn it into something awesome-ish. Animation HD is easy to use and has an end product that is easy to share.
Here is a hoping frog I made in five minutes. I will start with a screen shot. The tools should be familiar to anyone used to art type programs: different types of "brush", layers, fading, etc as well as the additional add/create frames part there at the bottom.
If you like to create new things this is an absolutely fun app.