I've been doing a BBS-inspired version of the PB Fitness workout once a week for the last 4 months. Prior to that I was doing the PBF twice a week, per Mark's guidelines,(since Nov 2010.)
I have progressed on all the exercises. I am now doing level 7 wide/close push-ups, level 4 dead-hang pull-ups/chin-ups, level 8 pistol squats, level 5 handstand, and level 7 spiderman planks. My progression got faster when I went to the once-a-week to "failure" regime.
And I am strong, but not bulky at all.