I'm very much looking forward to Chris Roberts' Star Citizen, which is shaping up to be one of the most epic space games ever. Chris takes the time to sit down and explain the economy of the game itself, in the video below.
As you can see, it's going to be a very complex game. If a certain plant needs materials (like metal) you can choose a mission to deliver it, or you can choose to be a pirate and kill someone who is delivering it. If you were to have a bunch of people on your side, you could be terrorists, taking out the deliveries which would drive the price of the materials up in the game.
This sounds like a very scalable game, where your actions actually have consequences for every one else playing. This is quite unlike most games we play today where our actions have "consequences" but they really don't.