I think its imperative in next gen mmo's that player owned shops. Yes i know thats nothing new but im pretty sure it can be expanded on and made more interesting. Honestly, im not even sure how games with player run shops work, and i will check it out in the future but.....
My ideal player run shops wouldnt be just selling items that have been farmed, but also trade skills. For example a player could learn blacksmithing and that wouldnt just allow him to make equipment but also to repair it too. As long as he sets up the anvil and has the necessary tools. Another example being a 'magic' shop that doesnt just sell farmed ingredients to sell but can train other players with spells using the 'new skill system idea by the in-game games' post i made at http://mmorpg.com/blogs/Artermis/072007/235_A-new-skill-system
Im aware that a player may not want to stand in his shop all day giving this service and for the simple selling of items/ingredients they wont have to, they can employ an npc to do this, or even another player! However to learn other players of new skills, then perhaps they do have to be present, so they could give some time to do this.
My game, i really want to have some kind of community feel to it, far too many times i see games that simply have too many towns/cities/areas that are ghost places. I want people to go to a particular town to do things and make a vibrant community, so that in those circumstances players will want to manage their shops properly, and not rely on 'npcs' to do things for them!!