As a humorous ancedote, Rich in Sac is a CHP officer, and said he caught someone in the fast lane doing 65 and someone coming up on them doing 85. He cited the first driver for reckless and/or hazardous driving and failing to yeild to faster traffic. Then pulled the second guy over for speeding.
Regardless, it does happen (probably not as often, but it still happens). Most of the time, an officer will pull you over to make sure everything is okay and probably not give you a ticket, but it is still on the books as an illegal offense if they want to pursue that route.