We were in Yellowstone in '12 and I seem to remember you had to stay 100 yards from bear or wolves, 25 yards away from all other wildlife. We came across a crowd of people just off the road, watching a grizzly sitting on an elk carcass. Two ladies kept inching closer and closer, trying to capture the perfect "Kodak moment", even as people were telling them not to get any closer. I told my wife to get her picture (from a safe distance) so we can get out of there without seeing what happens next.
Later, we were on a hike and had to go around a small herd of bison. We got within about 50 yards and I was uncomfortable even at that distance.