Maybe not today, but very soon. People are working on setting up networks now. To avoid getting arrested, the developers decided that they would release the client and not run the infrastructure. They will let the community run the infrastructure. That means we will have multiple competing networks for fees and arbitrators and such, but for right now the client can only connect to one network at a time. I imagine in the future that the client will have the ability to connect to multiple networks at the same time and aggregate all the listings into a single order book and just tell you which network it is if you click for details on an offer.