I feel that same way. But then again I'm in the Marine Corps. My last 20 years seems to have been for nothing considering what it going on over in Iraq right now.
assume "last 20" was on active duty? if so, seems like you and i joined the corps at about the same time. i didn't re-up after 4, but agonized over that decision for the last six months of my tour. in the end, obvious to me that "another four" might as well be 20, and i was too immature to make that decision. (sgt in echo 2/5, btw)