A Yahoo!/Interpret study of 4100 online video viewers is revealing a shift in online viewing habits. A 2009 study, online video viewing dropped significantly in the 6-9 pm daypart, arguably as they switched to more traditional TV channels. Now, 45% report watching some Web video during prime time "yesterday." (the study asked about use of online video in the last 24 hours)
For now, the impact on traditional television viewing (broadcast, cable & DBS) is minimal, and the focus of the study was not on whether this viewing was reducing traditional viewing, so you shouldn't necessarily infer that viewers are abandoning traditional TV media for online. At least not yet. But the study supports the idea that audience media use habits are starting to shift and that many viewers find value in terms of being able to watch TV programs and movies when they want, rather than when stations and channels program them.
Source: "Prime Time is Web Video Time?", VidBlog
"Online video shifts to primetime viewing," Gigacom
Press release from Yahoo! Insights