I think one of the reasons that there are so many apps that could be considered task management apps is that everyone has different ideas on what task management is. Also, there is some value in having local task items that are available in the tools that you already have at your disposal, ie Outlook. For us (shameless plug: http://www.ubernote.com), we wanted to have task lists inline in notes where we already had data, so we added the feature. Add one more app to the list....
Good luck with Ativiti
I have tried about 5 different apps, index cards, notebooks, etc but nothing has integrated into my life as easily as this (I already carry my iPod everywhere). Although it is expensive.
Have you ever wanted to use it for collaborative tasks?
I plan on implementing a GTD workflow soon. I'm using it mostly for daily to-do lists and managing projects.
Some people will find a solution which works for them, which fits in with their particular style of working, but for me at least these kinds of things require too much maintenance to actually compete with my current ad-hoc memory-based and almost certainly horribly inefficient system of doing things.
It would be better if there were more reader/writers for it (because it essentially is a file format) so that I could interact with normal people (who don't use emacs).
I really think a good software solution is the way to go. (Disclaimer: my startup is working on one)