...In fact, a landmark study released last year by the Project for Excellence in Journalism found that absent a crisis, day-to-day cable news ratings, contrary to popular belief, have been flat since 2001 at a baseline of more than 1.4 million in daytime (more than 2 million prime time) with little room for growth since most cable systems already carry the shows.
Fox News and CNN dispute this and say ratings are up. Audiences for network news remained steady during most of that period but have dipped lately, Poltrack says, probably because of Fox's growth...
http://www.usatoday.com/life/television/news/2005-04-26-network-news_x.htm
Give me time on this; I will try to find solid numbers.