A business model is the architecture of a business or project. It has four elements:

1. What compelling reason exists for people to give you money? (or votes or donations)
2. How do you acquire what you're selling for less than it costs to sell it?
3. What structural insulation do you have from relentless commoditization and a price war?
4. How will strangers find out about the business and decide to become customers?

The internet 1.0 was a fascinating place because business models were in flux. Suddenly, it was possible to have costless transactions, which meant that doing something at a huge scale was very cheap. That means that #2 was really cheap, so #1 didn't have to be very big at all.
 
Some people got way out of hand and decided that costs were so low, they didn't have to worry about revenue at all. There are still some internet hotshot companies that are operating under this scenario, which means that it's fair to say that they don't actually have a business model.
 
The idea of connecting people, of building tribes, of the natural monopoly provided by online communities means that the internet is the best friend of people focusing on the third element, insulation from competition. Once you build a network, it's extremely difficult for someone else to disrupt it.
 
As the internet has spread into all aspects of our culture, it is affecting business models offline as well. Your t-shirt shop or consulting firm or political campaign has a different business model than it did ten years ago, largely because viral marketing and the growth of cash-free marketing means that you can spread an idea farther and faster than ever before. It also makes it far cheaper for a competitor to enter the market (#3) putting existing players under significant pressure from newcomers.
 
This business model revolution is just getting started. It's' not too late to invent a better one.