If you have your own website or need to find contacts to sell your services/products, Facebook is the best service out there, and it's free. For the internet marketer, Facebook provides more personal contact for the viewer than a Twitter account does. By joining groups and interacting with these groups you will automatically grow your friends list in a way that has to do with your company. If you are posting relevent items to groups in your field, people will take you more seriously and realize that you know what you are talking about. This turns into sales in the future. When people need what you are trying to sell they will remember you more if they have had personal contact with you in the past and you gave them valid information that was generally helpful to them.
Don't get me wrong every so often you should post status updates and links about your business but you should also post things that make people realize you are a human being also. If all you do is try to make people buy your product you are not going to get any valid contacts and people will stop being your friend.
