(MediaBuyerPlanner) While CBS has consistently been a leading network among households and total viewers and will likely be the most stable of the networks at the May 17 upfront, its long-term success has come under question, with multiple hit shows' ratings declining, Media Life writes.

CBS once dominated Thursdays, yet its average among adults 18-49 is down 7 percent this year versus 2005. Also, the network hasn't found a good sitcom to follow Two and a Half Men. Its Tuesday 10 p.m. slot is having trouble as well, with four shows having cycled through this season.

"Of concern for [CBS] are the large declines this spring for reality programs Amazing Race (down 23 percent) and Survivor (down 28 percent)," said MediaVest's recent midseason report. "These programs are key for CBS to attract younger viewers as both have a median age in the mid-40s and are the lowest on the network."

The Super Bowl next year will likely compensate for some of CBS's minor problems until the 2007-2008 season.