I frequently draft -- I try to follow at a distance that allows me to stop if they jump on the brakes (which does happen sometimes). If the lane to my left is clear enough, I decrease following distance ride a bit behind the left rear so I can go to the side of the vehicle if they stop faster than I can. I like following pickups best. They're easy to see through and they punch a nice hole in the wind.

Although I like drafting, I don't think it's a particularly good idea. Debris on the road, metal plates from repairs, holes, and a number of other conditions make this practice a bit dangerous, particularly when it's wet. Sometimes when I ride, the next car behind me gives plenty of space so it won't run over the idiot cyclist when he falls. Others ride my rear wheel. Most give enough space.

Drafting definitely bothers some drivers more than others and I don't draft people if I think it bugs them. Aggressive drivers don't seem to mind, probably because they are tailgaters themselves. Also, big trucks as a group seem OK with it, but visibility is terrible. One thing I should mention is that the vast majority of my drafting is in heavy traffic where there are 3 lanes going my direction and no bike lane. I think tolerance for drafting might be greater where I am there because people don't want the bike holding them up.