Berber and other tightly-looped carpeting will often cause what you describe.  Because of the way it's woven, most carpeting has a "grain" to it, which when it's laid usually corresponds to the long-direction of the room when it comes off the loom.   You can easily tell by lightly brushing your hand across the carpeting.  In one direction it will feel smooth and the nap will lie down as you brush it.  Going the opposite direction you'll feel the nap bristle a bit against your hand.  Vacuuming "against the grain" will sometimes cause the nozzle to "chatter" or skip.  Once you've determined the north-south direction of the nap, try vacuuming as much as you can going east-west and you'll avoid the problem.  This was part of carpet selling 101 back when I worked in home furnishings.

What an idiot! 

The brushroll isn't skipping.  It's the shape/design of the nozzle plate itself and how well it glides vs gripping/snagging on the carpet nap.  Some nozzles will do it more than others.  Even some straight suction nozzles will skip.  Try reducing the suction a bit, if the vacuum you're using allows that to see if that makes a little difference.