An average Facebook user is eligible to see more than 2,000 pieces of content per day

"On average, a Facebook user is eligible to see more than 2,000 pieces of content per day. That’s a lot of content. We’ve tried showing that content in chronological order, and have tested that every time we have, the overall engagement would decrease dramatically, and users would actually see less content because they didn’t find the content they were seeing as interesting and were missing the important stuff that maybe was posted hours ago, so we take each of the 2,000 pieces of content and rank it based on the probability that you’re going to interact with it. On top of this, sponsored content is added in and may bump organic content down, but we’ve minimized the decrease in engagement and make sure to not show too much of this if the user reacts to it negatively."
Source:  Reuters interview with Facebook's Vadim Lavrusik, 5th March 2013
Note - if an average user has about 350 friends, then each friend creates about 6 pieces of content per day (including Likes, pictures and comments)