There is an amazing post on Socialnomics on statistics related to social media. Have a peek at the embedded video. The key takeaway being - social media is not a fad, even if we halve the statistics from the post, we are looking at a Juggernaut. Ad serving will undergo a fundamental change in the next 3-4 years with more dollars moving into social media away from search and display. Goog is going to suffer and Y! will most probably cease to exist.