Great! It's nice to connect with people doing similar things. I also record priorities and am happy with it. It's one of the things that helps towards being able to see a list of things I can do now, want to do and want to have done; and towards getting done the things I want done.
2. As a means to separate tasks into three categories of importance, however, i.e. priority in the second sense I mentioned above, I think ABC is very, very good indeed. I do this, and am superbly satsified with it:
Cool! Based on your post and goncalomata's, I get this idea: when in a given context, one might want to see a list of various actions for that context plus high-priority actions for other contexts.
When I select additional tasks from the list that match a particular context etc, I also always check the most important tasks (A), and compare and choose. This gives the most important tasks a chance to always get noticed and considered.