These three are all you need to understand. Facebook is huge, learn it, use it and adapt with it!
1. 93% of adult US Internet users are on Facebook. source: BlogHer, April 2011
2. One out of every eight minutes online is spent on Facebook. source: ComScore, February 2011
3.The average Facebook user spends more than 11 hours per month on Facebook. sources: Bureau of Labor Statistics, June 2010 & Facebook Press Room, 2011
via 12 Essential Facebook Stats [Data].