My uncle (who lives in the UK) did this several times in the 1990s (in his mid 30s) as a cheap way of taking a road trip across America. I'm not sure of the exact financial arrangements, but I was under the impression that they paid him reasonably well.
People are certainly paid for it in the UK- they're called 'trade plate drivers'. If you see anyone by the side of a motorway trying to hitch-hike while holding red and white number plates, it's a trade plate driver trying to save on their return journey expenses. They get picked up a lot more readily than scruffy hippy students, in my experience.