Putting it simple, duplicate content is content that appears on the world wide web in more than one place. Is this such a big problem for the readers? Maybe not. But it is a very big problem for you if you are having duplicate content (internally or externally) as the search engines don’t know which version of the content is the original one and which one they should be ranking.
Facebook ads are a great way to get highly targeted traffic to your blog (landing page, fan page, what ever). Although not a free traffic source, it is a great one. The price is not very high and I think it is pretty acceptable considering that you can choose demographics of Facebook users that will see your ad. I had great success getting traffic that converts on one of my niche sites.
Beyond organic and direct traffic, you must understand the difference between all of your traffic sources and how traffic is classified. Most web analytics platforms, like Google Analytics, utilize an algorithm and flow chart based on the referring website or parameters set within the URL that determine the source of traffic. Here is a breakdown of all sources: