I suppose since I play mostly on large size maps, and play typically a domination-style game, I end up capturing all enemy cities and end up with 100+ cities easily in a game before I reach the 66% population/land domination limit.
once when I played on a huge real world map, I ended up with over 200 cities, took forever to get through a turn -- it gets way too complicated once you reach around 40+ cities and I will just let the AI manage my citizens and cities since it's just too much effort to manage each city for the sake of a game