I completely disagree that priority is too nebulous to record. While it may be the 4th factor in the GTD decision process, once you are in a context, know your time available, and know you energy level - you need to decide which of those 100 tasks that fit the current criterea to do! I might have a high energy right now and am at my computer ready to work, and have a list of 100 30 minutes tasks. How can you possibly do that without recording some sort of priority?
If priorities change over time, then reprioritize! Prioritizing is an essential part of managing your life and time. Perhaps your list is small enough that you can glance at the whole thing and pick out the top priority ones, but mine is not.
Incidentally, I just found a solution that pretty much solves this problem for me. I can tell you, priorties make a HUGE difference in the usability of OmniFocus. Look at the solution (and my longer rant) here:
http://forums.omnigroup.com/showthread.php?t=11529