I especially like the habit tracking. Not a lot of similar products have a feature like that, and the fact that it breaks down the process of creating a habit for you is really neat. I actually read The Power of Habit a while ago, but never really succeeded at putting it into practice.
If I want to put my important data into an app like this, I want to be confident that I'm not going to lose it. One feature that I missed from the demo is the ability to undo actions. For example, I accidentally marked a habit as done when I meant to click the "+1" button; then I had a "fake" habit in the Achievements tab and had to manually remake the habit. It would be nice if I could just press Ctrl-Z instead.
However, I love how easy it is to get started. The fact that you can just start using the app right in the browser and then sign up when you're ready is exceptional UX!
I signed up for the newsletter, and would definitely check this out again when it's a little bit more robust. I hope you get to keep working on it!