I am not kidding at all.  Its barely faster than running, gets stuck on tons of tiny geometry, and while it has some small advantages like an initial reduced agro radius, if I am not racing to a world boss, I mostly don't bother with it.  It sucks.  As Chris mentioned there is a stuttering issue.  For me, after it hits something in the geometry, it seems mine will trot at times and not run under any circumstances for a while; Its like WTF WHY IS MY HORSE WALKING.  That sucks particularly when its mobs, who can definitely knock you off your mount.
It's just a shit implementation of a mount.  Maybe my Barbarian needs to lay off the barbells and twinkies. Again, its my opinion, your experience may differ.