I have been using it for a week in two different projects and I'm impressed. Does what it says very well. Building the wireframes and prototyping the navigation is very fast and painless.

The only drawback is that it seems a bit slow sometimes on my MacBook Pro Intel 1.83, I suppose it is because it isn't running native. I would be really glad for an Intel version, but that is a minor issue for me, I am really happy with the program.