Social media marketing used to be divided into two factions. Social networking sites where you could connect with others, become perceived as an expert in your niche, build your own brand, create a great customized profile, add 'friends', join or create 'Groups', comment, message, add images, videos, and other media, etc., and link building sites - where you could do your content publishing - put your blog posts, articles, photos, videos, and people sometimes had the option of voting your content up or down.
There wasn't a lot of 'social networking' between people (at least not at first) on the link building sites, and the main attraction of these kinds of sites was quality content. Also, in a social networking site, you could make a rich, full profile but in a link building site, you didn't have a big opportunity to customize your profile.
Until now. Now, you can have a Facebook Fan Page. Facebook is included in the "social networking" sites I talked about above. But Fan Pages include the elements of a "link building" social media site. All in one package. And, you can have as many Fan Pages as you want, in whatever niche you want.
Facebook has recently reached 500 Million active users. On average, at least half of those users log into Facebook on any given day. The average amount of 'friends' a single user has is 130 and, more astonishing, users visit Facebook for over 500 BILLION minutes per MONTH. That should answer the question, "Why Facebook?"
GROUPS OR FAN PAGES?
Well, this is really a no brainer, but it's good to have an explanation of the differences, because each has its own functions.
The best description I've seen is from Mashable:
"Groups are great for organizing on a personal level and for smaller scale interaction around a cause. Pages are better for brands, businesses, bands, movies, or celebrities who want to interact with their fans or customers without having them connected to a personal account, and have a need to exceed Facebook’s 5,000 friend cap."
SO, WHAT EXACTLY ARE FAN PAGES?
According to the Facebook Pages Manual - which you can download and use for guidance in setting up your Fan Pages - Pages were added to the Facebook milieu so that businesses, organizations, bands, and celebrities could keep in touch with their fans in "an official, public manner."
For us, the key word here is "businesses" because when we use a Fan Page for a niche specific keyword/product, that is our business.
With a tightly keyword focused Fan Page, you will be indexed fast by the search engines. Your individual fan page will let you be recognized as an expert in your niche with exposure to maybe thousands of people each day, build your list, generate traffic to your blogs or websites, and much, much more.