According to a Nielsen Company report just released, 2008 was the year that social networking really took hold in the world, surpassing email usage and growing the fastest not amongst the youngest Internet users, but the middle-aged — those in the 35 – 49 year old age range.

While search engines and general interest portals like Yahoo! still have the largest reach (85 percent), “member communities” — which includes not only popular social networking websites like Facebook, but also blogging websites — reached 66.8%. This was the largest increase — 5.4% — of any sector measured from Dec. 2007 to Dec. 2008, and double the increase of any other sector.

Even though email was surpassed by these “member communities” websites (including blogs), email still enjoyed the second largest bump of the five sectors measured — a 2.7% increase from 2007. So even while social networking websites expand their reach, people are still turning to email as much as ever.

However, as I looked over the data in the report, one site really stands out — Facebook. Its growth increased an astounding 566 percent in one year! Nielsen estimates that by the summer of 2009, middle-aged users will surpass college-aged adults who use Facebook. (Which begs the question, where will all of those college-aged students head to next?)

Despite having a unique global audience of 108.3 million people in Dec. 2008, Facebook still has yet to find a way to generate revenues that are in keeping with its audience numbers. Just imagine if a TV show had 108 million viewers week after week… It would be the biggest hit show of the season. And this isn’t just for a single month — this is month after month of sustained growth.

Nonetheless, it’s unlikely anything can stop the social networking juggernaut. People really enjoy sharing their lives with others, even if it’s just their friends and family. And there’s little sign this is going to change in the years to come.

Read the Nielsen March 2009 report: Global Faces and Networked Places (PDF)