I think graphicdetails gave a very good answer on how to approach things. I follow a similar mantra, but with perhaps some differences.

I have been doing GTD for a long time. One trap that I have seen myself and many others fall into is that one can become very good AT GTD versus getting things done. I know that sounds silly, but this forms the basis for a lot of the negative comments by people on blogs about how GTD makes one very organized, and doing many next actions, but really not making a lot of progress on the large projects. I have posted on this before -- does GTD make one very busy, but not necessarily productive.

So here is how I approach major projects. I keep a next action on my lists as a bookmark only as to where I have left off the last time I worked on the project. When I have decided it is time to go into "project-centric mode", I perform that next action and afterwards just keep working on the project. I do NOT go back to my action lists as the only active action I had on the lists is done. One needs to focus to get hard work done! I may work on that project for an hour, a morning, or a day. But always off of the project support folder. When I am done for the time being, I think of what the next action should be, then put that action -- and that action alone -- on my context lists. A bookmark!

I do have a number of one-off actions on my lists, and of course when I am working in that mode, I scan my action lists for things to do. THAT is what I see the action lists for -- next actions only!

One other thing I do is to set start dates and target due dates for all of my projects. This way, I have a realistic timeline for when things will get done. Of course it is not fixed in stone as things change, but in this way, I can tell people when they ask me when I might have something done -- AND -- how much work I have on my plate.

At any rate...my approach to projects and integration with GTD. Be careful, folks...do NOT just become good at GTD...that is not at all what David Allen expects you to do -- it really is about focus and getting things done!

Best wishes,
-Longstreet