screenshot courtesy of Appbrain
Basically, you get Flash-type animations demonstrating the various poses, and gives you several different practices, with choices of duration and difficulty. The app claims over 100 different illustrations, and is completely self-contained (no network access needed). On the other hand, it's also 20+ MB download and install.
While the idea of Yoga instruction in a pocket is fine, Yoga really needs to be on a TV (DVD) or even a live instructor. This is better than nothing though.
This is a paid app, but were given away on Amazon for a day. It's okay, but not great.