I hear them used *all* of the time. That is, the major geographic divisions, at least.
D'hara must be quite different then. I've played through pretty much all of SA and few times in Luria. That is quite a large player base. I don't remember hearing any custom made topography names in SA, and in Luria only one player was mentioning them. The only other discussions your character might have are various guilds and rulers chit chats. Both of those are the minority I'd say, so maybe not the greatest frame to make an objective conclusion.
The problem is that the major source of the player invented topography is the Wiki, a source which few people actually read. I just think that if the main source was the game itself that they would be more acknowledged and much more used.
