I'm using doit.im now for half a year and I generally like it a lot. Keep up the good work.
The other tool I'm keeping an eye on is NirvanaHQ. Features that they offer which are for me missing in doit.im are:
- area selection (doit.im has tags but a simpel selection that filters all lists saves a lot)
- task ordering: to be able to add all tasks per project and select the next ones to be visible. I tried something using priorities or the someday list to put the non-next actions in but this is too cumbersome.
- contact filtering (contacts can be added but only for handing over actions, I would like to filter on agenda items and waiting for actions per contact. Tags can be used but are only an in between solution)
- FIlter options: I like the filter options and that you can select two conditions per filter.
It's a pity however that I always "lose" one condition by having to select the status as uncompleted. I'm typically not interested anymore in filtering my completed actions. Having another condition or making the (un)completed selection simply selectable by a checkbox for example would help me a lot.

I hope you are taking at least some of these into account for you next releases. Do you have a target date for a new release already ?

What I currently like a lot about the tool, the list is not complete: reminders, google cal integration, drag and drop, the mobile android app (quick entry !)