Twitter lets us tell the world what we are doing. Foursquare allows us to broadcast where we are doing it. Empire Avenue let's us determine how much we are worth. That's essentially the premise of this quirky and somewhat addictive social system modeled after the stock market and loaded with game mechanics that reward you for a variety of participatory behaviors both on the network and across others.
Like Twitter and Foursquare, the network makes very little sense to the first time participant. It's more Foursquare like in the sense that it functions as a game—however it increases your "worth" based on the investments you make in others as well as your activity on the social networks that you connect to it. First impressions? I'm not seeing a practical use but it's a lot more fun in many regards than Facebook.
One application I could see potentially. For brands looking to gauge their social currency via the level of activity across networks and put a score to it (similar to something like a Net Promoter score), there are some interesting pieces of the platform which could potentially work this way. It's too early to tell exactly. I'm on it as are many of my friends—like the beginning of any social network. And just like all networks it will either gain some level of adoption or fade off into the sunset. Are you trying it out? If so, buy me while I'm still affordable. :-)