From the latest survey by the Pew Research Center

# 8% of internet users said they had ever visited a video-sharing site such as YouTube. A year ago, in December 2006, 33% of internet users said they had ever visited such sites. That represents growth of more than 45% year-to-year.
# 15% of respondents said they had used a video-sharing site “yesterday” — the day before they were contacted for our survey. A year ago, 8% had visited such a site “yesterday.” Thus, on an average day, the number of users of video sites nearly doubled from the end of 2006 to the end of 2007…