may be I can help with NoteStudio. You could imagine various implementations of GtD using such a Wiki system. For me, it must be simple to use and FAST. Enter fast, process fast, review fast. Inspired by many contributions from this as well as from various other groups and websites, I created a set of GtD templates for NoteStudio. You may use these as a starting point to get an impression on how GtD could be done by a Wiki system, especially NoteStudio.
You will find these templates on the DogMelon website:
The same templates can be found in the files section of the Yahoo group GtD_Palm, together with some screenshots taken from the PC version.