It displays text and that's about it. Jumps to beginning any time you show/hide the interface.

The Good: It's OK. It works.
The Bad: But it's as ugly as sin, and as someone else said, you won't want to read a whole book in it. I don't think it shows any images.
and...
The Ugly: You can't use your keyboard to move up or down through the .mobi, you have to use the scroll bar.