I love these things. They're brutal. It's like a big, heavy ab movement instead of a bunch of high-rep crap. Plus, isometric ab contractions are said to hit muscles which would otherwise go untouched by dynamic contractions alone.
Let me make sure I have needsize's routine right:
hop on a decline bench, lean back to 45 degree and hold for 5 seconds. 5 of these = 1 set. Do 5 sets. Is that right?
Do you hold your body in a "crunch" position or in a straight line from hips to head?