People rarely do the speed limit here, mostly people do 5-8kph over, but they get caught for it, (revenue raising) and it's costly.
I mostly do the speed limit I guess, overtaking on country roads is the exception. I once got $2300AUD in fines for speeding three times over two weeks and lost all my points except one or two which wasn't good. (Points don't come back for three years). If I lost my license I'd lose my job the same day so had to be careful (for three years). All good though, and it built a habit of doing the right thing.