Like Mark I've also found it useful to make NAs extremely simple. Just the other day I managed to move a stale project forward to by changing a slightly-complicated-and-vague NA to "Go to kitchen" (a bit like Mark's "Open Excel"), which really was the next physical action. By doing that NA I easily worked out what to do next and got the project ticked off after having it on my project list for many months.
Yes! I just got a huge amount of work done on a painting design that had been waiting for months by making the next action "take a piece of charcoal to the living room drawing board."