Interesting online video statistics from: http://www2.cio.com/cmo/metrics/viewmetric.cfm?METRIC=866
A little old but still relevant?

October 26, 2005

In June 2005, more than 94 million people in the U.S., or 56 percent of the domestic Internet population, viewed a streaming video online. The average consumer viewed 73 minutes of streaming video content per month. Interestingly, male users, who represent 50 percent of the total online population, accounted for 61 percent of video streamers, but both male and female viewers spent roughly the same amount of time watching online video content. The 18 to 34 year-old male segment, which is the most difficult to reach through other media, watches for longer than other population segments at 84 minutes per viewer. The daytime was also the most popular time for viewing streaming video from 10 a.m. to 4:30 p.m.

Source: Comscore Networks