Back in the days me and couple friends played Silkroad, the queues were massive. I had to log in and sometimes wait 2-3 hours to get in the game, so most of the time my character was online afk just because if I leave I had to wait again.
In Silkroad you had the mechanic to create a stall with your items and others could click on the stall and see what you are selling. This was so new and interesting then, I was really impressed by it.
But now when I think about it, when I went in the city my PC struggled very hard because of the thousands of players with trading stalls.
I love the idea and it makes the whole player experience very immersive, but if everyone can do it, the cities will be flooded and your FPS will be close to 10-20 when you enter :D
Localized markets is another thing I like very much, as Sylandir said this will bring meaning to all cities and players will have to look around every market in order to find the best deal.