I have to admit that I like the idea. You just type text into the editor and by using the markup characters the results turns into a nicely rendered structured list of stuff that needs taking care of.
The most compelling feature is that the content is stored as a mere text file that can be put on the dropbox so that other instances of Taskpaper can access the same to-do list. Just let dropbox take care of the syncing!
And sure enough, there is an iOS implementation of Taskpaper available from the iOS Appstore.
The downside, at least in the current state of the app, is that there is no notification of due to-do items. On the Mac, this would ideally be supporting growl or at least it would display badge notifications in the dock icon. On iOS, the canonical way of notifying obviously is, as of iOS 5, Notification Center.
Pun not intended.↩