The Three Screen Report, conducted by Nielsen, reports that "the average American watches approximately 153 hours of TV every month at home, a 1.2% increase from last year.
In addition, the 131 million Americans who watch video on the Internet watch on average about 3 hours of video online each month at home and work. The 13.4 million Americans who watch video on mobile phones watch on average about 3 ½ hours of mobile video each month." Click here to read the entire report (pdf).
In an encouraging note for the television and cable networks, a recent survey found that only 8% of respondents (18% teens) watch TV online. So, at least for now, it seems network and cable TV will continue to be the primary screen--at least for a little while longer.