I would love it if players couldn't summon their mounts while inside a city, village or town. To me it is very immersion breaking to be strolling down the path, and suddenly get ran over by multiple other players, rudely charging through the mass on horse back, not seeming to care at all who they're running over, player or npc alike.
You search and search for something, never realizing it is within and always has been. You can not find it, you can not understand it, you simply accept, and believe, and it will grow. - Heretic's Faith, Randall N. Bills