I use my emails as action(s) reminders because I find it quicker to define the actions upon email re-read than to diligently convert them to actions in my main list manager (OmniFocus on the iPad).
My folders currently look like this:
So there is a degree of up-front decision making, but not too much. I find the "Data entry" and "Reply" folders the most useful.
I also like the idea of simply archiving emails right away as reference or project-/action-support material, but couldn't work out how to quickly get the various next actions from my email into OmniFocus (given that I'm often in email on the computer - sometimes a Mac, sometimes a PC - but pretty much only interact with OmniFocus via the iPad).