My favorite drafting experience was when I was on one of my first century rides and a huge firetruck got stuck behind a group of cyclists negotiating a narrow road. Fortunately, the firetruck wasn't in a hurry so it just went along at 30-something waiting for the other cyclists in front to move over. Even more fortunately, I was in a later group of cyclists and got to draft behind the truck for 1/2 mile. WOW! that was a blast!