OneMarket is nothing special at all, anybody can create a classifieds website to list items for X coin, and have a script into the wallet displaying the listings on the website...it piece of cake and nothing special...the real problem with something like this is the incentive to use such a thing... why should I sell my things for cloakcoin, this is the real question...I can sell them directly for Bitcoin in the near future on eBay...
The whole point of it is that it's not a website controlled by anybody. It's decentralized and can't be shut down. Look to Silk Road to see why this is important, especially for a coin with another major selling point being anonymity.