On a recent road trip, a cop pulled us over to let us know that we'd been in the left lane for a while and in that state, the left lane was solely for passing people. He noticed our out-of-state plates and figured we didn't know. He was right: in my home state, I generally sit in the left lane for ages when I'm going a long way, since I drive rather fast.
In what states are you not supposed to linger in the left lane? I don't want to get in trouble when road tripping in the future.