I don't know much about the GTD Add in software--I only implemented the PDF white paper. But I got frustrated quickly with no real way to track the many tasks that are associated with a project.
Bill Kratz' method comes the closest for me. In Outlook on my desktop, he has an excellent sytem for tracking projects, with a complete view and history of the associated tasks.
Synching to my Palm is another 'story'. Since installing Chapura's Key Suite, I have a lot more flexibility. All my projects now show up as a separate category (Projects) on my contact list. I can view any associated notes that are part of each project, but "alas" I cannot view the tasks that are connected to each project--I am hoping that there is a way to do this with the newer Palm synching software, or a different way of configuring MS Outlook.
An interesting sidelight: I am re-evaluating the whole quest to synch Projects to a PDA. Why?
GTD's usefullness in a PDA is pretty much restricted to 2 task areas--calls that can be made on the run, and "errands" that can be done while 'out and about.' Data collection could be a third area, but a PDA is not strong in this area.
So as long as I can get all of my tasks (including those that are project spawned) synched to my PDA, why should I worry that the project isn't there?
I think you're right about the Add-In being used pretty much for e-mail linking, for those who have adopted Bill Kratz' method for project control.
My big problem with GTD's method--a Project is not a task, no matter how well you re-name or disguise it. I personally could not get used to seeing Projects co-existing on the same list with my Tasks.