Some feedback, tried to contact you directly but couldn't find a email address.
I use this method of task mgmt at work, some suggestions on features to allow full functionality on the iphone.
1. Allow me to create additional custom categories beyond To Do, In Progress and Done. No limit to the number of categories.
2. Allow me to go to a page of all the tasks for a category. I could easily have a dozen or more items in a category.
That's it. I think you have something really great here, simple app for managing tasks. Feel free to contact me at me (at) mikebrandvold.com. Would love to help you improve the app!