Nielsen recently released some summary numbers from last year's TV prime-time viewing.
'Reality' shows accounted for more than half of all viewing, gathering 56.4%, up from 49.4% for the previous year (but down from its high of 77% for the 2007-2008 season). Scripted dramas account for 23%. Sports programming accounted for the next highest proportion of viewing, at 20% of prime-time viewing. Nielsen reported that total primetime audience numbers remained high, just short of 200 million.
Source - Reality TV Grabs Most Viewers, Sports Nabs 20%, MediaDailyNews