My favorite apps, the ones that slip easily into everyday use and stick there, just start with plain text and add some extra sauce. VoodooPad is a great example, and Hog Bay Software's new app TaskPaper is, too.
All the extra stuff in iGTD was appealing, but I left tasks in the inbox for weeks, and never reviewed much of my vast forest of projects. I eventually fell back into tending short lists in Stickies, with titles like "NOW:" and "BY TUESDAY!:".
When I moved those Stickies lists into TaskPaper, all I had to do was copy and paste - it uses the same format I do when I get lazy, and that has to be a good sign. I haven't found a reason to jot a note somewhere else yet.
Moving tasks from iGTD was more sobering. Half those "next actions" had been done for weeks, and the other half were clearly scheduled for next Neversday. As Merlin Mann pointed out, switching apps is a good excuse for a real review.
TaskPaper adds automatic formatting, tabs, search, and a bit of hyperlinking to plain text. Tasks are lines that start with a dash, and can be tagged by starting any word with an at-sign. Clicking a tag starts a search for that tag. I use them in a couple of ways - as contexts, and for scheduling. They can really be anything that makes sense as a visible search keyword.
I have been keeping a few tabs open - one to edit tasks, and a couple others with live searches to look at what's on my plate. When I want to schedule something, I'll tag it as @now or @tomorrow - I have those two as open tabs, and as I work I keep the @now tab open. Other tabs come and go to look at contexts, like @email or @errand.
I like that the tags can be part of the sentence, so I don't have to tab through a bunch of controls to set tags - I just write something like '@email Bob @home'... easy.
I also set up an inbox project (by typing "Inbox:", naturally) to collect notes quickly, and that's worked pretty well so far.
As with any 1.0, there's some room for improvement. It's not very scriptable, but it is plain text, so it could be worked around. Quicksilver integration was important with both kGTD and iGTD, and I'm not sure yet if I'll really miss that here. It can clean up tasks marked as done into an "Archive" project, but doesn't yet note when they were finished, if that kind of thing matters to you. Finally, I'm not sure what the best way to sync with other devices would be, but there is a web interface in development - maybe that would be a good iPhone option.
TaskPaper is a solid, clear, and nicely minimalist app. Over the week I've been using it, it has made keeping to-dos in one place too easy to avoid, and added just enough functionality to sort through them without being distracting.
Note: When I downloaded the 1.0 release, I found a conflict with TextExtras and wrote a bug report. In reply, Jesse sent me a complimentary license. Nice guy. I was going to write about it anyway, but I thought I should mention that I got it for free, as a surprise.