According to compete, 2 out of every 3 people online visited a social networking site in June, and the number of people visiting a social networking site has grown 109% since January 2004 (driven mostly by MySpace).
Nielson//NetRatings claims that MySpace has achieved year-over-year growth (July 2005 – July 2006) of 183% compared to 23% for Google and 13% for eBay. MySpace also hit the 100 million account mark on August 9, 2006 at around 7:41 am EST. As I mentioned earlier today, del.icio.us is also showing tremendous growth with Hitwise claiming that Del.icio.us traffic has doubled since January.
The point of this post is not to obsess over exact numbers, many of which tend to contradict each other; however, it does show that social networking sites are continuing to grow at incredible rates. As markets mature, the growth tends to eventually level off as the market becomes more saturated. For example, when DVD players were new, the growth was rapid as people bought their first DVD player, but the growth has leveled off now that everyone owns a player and sales continue mostly in the slower growth replacement / upgrade market. I would expect social networking to level off as social networking moves from the early adopters into the masses; however, it is also possible that it will continue to grow at a rapid pace if early adopters keep moving to the next hot site bring the masses along behind them.