I always ride on professionally built and maintained trails (places like Albion Hills, Hardwood Hills, Mansfield for those of you who are in the Toronto area) and I find that everyone is super-polite and friendly.
Much of the riding I do is on single track and everyone follows direction indicators and will let you pass them if you are faster. The best part is that trails are rated, and the more difficult trails (such as Gnarly at Hardwood Hills or the "24-hour" route at Albion) are almost always deserted.