An area of Facebook which is making several companies huge amounts of money is the applications that run on Facebook. There is for example, a mafia game on Facebook which has been hugely popular with millions of users. And there are many other companies making huge amounts of money with Facebook apps (applications).
So what opportunity is there for you?
Firstly I would suggest you get on Facebook and look at these apps, see what is happening and see which are the popular ones and ...
