"Because the top social media sites can deliver high reach and frequency against target segments at a low cost, it appears that some advertisers are eager to use social networking sites as a new advertising delivery vehicle," comScore VP Jeff Hackett told Reuters.

The number of ads being viewed by social networking users isn't a surprise, according to other analysts, who point out loyalty to social networking sites -- along with large user bases -- with No. 1 social networking site Facebook has more than 200 million active users, with around 100 million Facebook users logging into their accounts at least once per day.

Some advertisers have been hesitant to use Facebook, MySpace, and other social networking sites, as user-created content can sometimes be too risque and offensive.  Advertisers still reach a large audience while paying less than advertising on Yahoo, Google or other web portals, which makes it worth the risk of dealing with potential scandals related to social networking sites.

"For big, national brands it works just fine, just like TV," according to Sanford Bernstein analyst Jeff Lindsay.  "It's a huge, huge volume game."

Internet advertisers have had a turbulent year, with the struggling global economy limiting how much advertising money is available.  Companies such as Google and Yahoo continue to look for new advertisers -- especially Google's hunt for YouTube advertising -- but there are so many companies looking to cash in on advertising.