According to MarketingCharts.com, as of November 2009 Facebook has 46% of the US market share of social networking site visits.
Does that mean you need to have a Facebook presence, because nearly half the people you want to reach are on there? Well, is your target audience all US social networking site visitors? (This is a trick question. The answer is NO).
Don’t get caught up in trends if they’re not relevant to your specific objectives and audience. Respect your new or potential constituents and refine your strategy to fit them, not the amorphous majority of all Internet users.
That’s why I like the Forrester Social Technographics Profile Tool. While it still makes some broad generalizations about Internet usage, at least there are some distinctions made. Obviously, direct surveying of your audience will help even more in ensuring your strategy fits with their needs and behaviors.