As far as speed limits go, some are indeed quite arbitrary, and some accurately reflect an appropriate speed on the road given the conditions. I'll "fudge" my spedometer by ~5mph when it's obviously an arbitrary number set only for revenue generation, but I'll only go so far; "professional courtesy" goes both ways, including the courtesy of not giving the radar cop a reason to notice me in the first place. Other times, I'll go under the posted limit, simply because -I- am not comfortable driving at the limit under the conditions.
All that being said, I absolutely abhor the idea of traffic tickets. Either something is wrong, or it's not; with a payable ticket, you're simply demanding people pay an indulgence to the state for exceeding an arbitrary number.