A few early observations...
1. The autogenerated list display ("inbox" through "complete") takes up too much screen real estate. All but your first two custom lists will require scrolling to access - this is actually a fairly significant pain.
2. The font for list items is too big, most entries WILL be clipped.
3. Adding a new task requires a completely unnecessary extra tap to get to enter the title - clicking the "+" sign in a list should take you right to a blinking cursor with a keypad to let you enter the title.
4. Allow manual sorting of lists. Manual assignment of priorities is probably preferred over any of the current 3 sort options.
I imagine the VAST majority of users would appreciate these changes that would make the program even more efficient. I think if these changes were implemented this app would be a valid compitetor with the Listmaker app which is substantially more expensive and currently more buggy than this app.