A "project" in GTD essentially is just a "big task", something that has tasks in it, and will be totally finished and checked off one day.
But not all tasks belong in projects. And Doit does not force you to keep tasks in projects. But I have chosen to always put all tasks in projects. Those tasks that do not belong in real projects I put in a phony "project" named after the Area of Responsibility to which the tasks belongs. These phony "projects" are permanent. They will not be checked off as completed. They just serve as buckets - I get a "project name" that is visible in the lists and which I can use for sorting etc. That's all. But I find it convenient.
According to David Allen it is common to have maybe ten AoRs in your work and maybe another ten in your private life. Personally, I have defined only eight AoRs all in all, because It think it gets too messy (long lists, too granular for my taste) to have more (I have tried).
For my private life, I use only these three:
\ P-MTR The responsibility to look after the family's material assets and services, including housing, cars, bank accounts, electricity, phone, insurance etc
\ P-AMB The responsibility to represent the other family members and look after their interests in their dealings with other people, including their colleagues, employers, teachers, banks, authorities etc. I also include here (to avoid having too many AoRs) my personal obligations relating to various non-business associations and entities.
\ P-MAN The responsibility to look after myself personally, for my own personal pleasure or development, or for upholding my own personal interests in relation to the family members. I also include here (to avoid having too many AoRs) my personal obligations as an educator/coach/influencer of the other family members' personal behavior and personal development.
I think of my AoRs as "roles" rather than as "types of task". For example, if I need to read a certain book, this could go under any of the above AoRs, totally depending on why I would read that book - in my capacity of what. (If I would want to somehow separate "reading" tasks from other tasks I would see this as a contextual requirement - need a book, need light, need a seat etc - and use a context/tag for it.)
For my work (business) I have five AoRs, also defined as roles. Two of them are for two specific long-term joint ventures with other companies, one is for my own ongoing consulting business with various clients, and one is for the general management and "infrastructure" of my company (furniture, computers, bookkeping, phones etc). And the fifth AoR I am planning to drop.
Interesting, I have considered doing this as well. But where do you put your short term projects, are they just mixed in with your AOF's?