In 2007, CBS' last time with the Super Bowl, the advertising time wasn't sold out until a couple of days prior to kickoff, so network executives are pleased with this year's results.
The U.S. economy has a huge impact on the success of network sales efforts. In 2008, FOX was sold out of Super Bowl inventory by October 2007. The advance sales were indicative of a strong economy. For 2009, NBC started out strong but ended up having to practically beg advertisers to participate given the economic downturn which hit a few weeks prior to last year's Super Bowl.
CBS' approach, over the past several months, of trying to create customized packages for advertisers has paid off. Rather than go out with an announced firm price, CBS chose to publicly state its desire to work with advertisers on the right package and price. (As previously reported, CBS has been seeking $2.5-3.0 million for a 30-second commercial in the game broadcast.)
If you're still interested, CBS does acknowledge having pre-game inventory still up for sale. However, many of the half-hour blocks leading up to the game have title sponsors, thus causing hesitancy among some advertisers who may still be interested.