OK.
"as Jonas pointed out drag-n-drop would be a pain to use with long lists if you have to drag to the end/beginning"
Have a look at 2Do for iPhone. Fantastic layout and looks. No need for the looks but layout would be a great inspiration. It's got folders with drag n drop. At the left instead of at the bottom. That way you can work with a today-screen (more about that below).
The way Geetaks is setup now you could have a move-area between [sort:none] and [Purge]. You drag the task down to this area and a screen pops up and show the lists (or defaults to the today screen) that you can move it too. Maybe not so good if you've got 10+ lists. But indenting is the solution to having too many lists anyway. Your app is the only todo with indenting/subtasks right now!
"Could you describe your GTD implementation in more detail? "
http://norbauer.com/notebooks/ideas/notes/the-psychology-of-omnifocus
I think this is a good description and a good article (even though it's about an advanced competing product, too advanced..). It says why just having lists with items only is a bad idea (and why you'd need a separate today-list or contexts). That's why moving things around is needed.
"you could make a special "today" list where you move things into at the start of the day?"
Yeah. That's what I'd use. But a quick way to move things to that special today-list should be super simple. I'd have to buy your program first to see if it's simple or not.
I'd be willing to pay for the program (done) + $100 if you could have a today-screen/list-move with drag n drop - and if I could use a beta version so that I could use it earlier (soon). I'm not sure if that's a lot of work with Apple to make it happen. It could be a great way to get around the approval process if that's how it works (I'm not sure).
If this is not of any interest I'd love to be a beta-tester and be able to use the indenting/move and report bugs. I've read that it speeds up the approval process.