Two interesting data points:

New York Times: Studios Rush to Cash In on DVD Boom (via Scripting News):

Between January and mid-March this year, Americans spent $1.78 billion at the box office. But in the same period they spent $4.8 billion — more than $3 billion more — to buy and rent DVD’s and videocassettes.

Ipsos News, Downloaders Expanding To Motion Pictures And Music Videos (via David Akin):

New findings from TEMPO, Ipsos-Insight’s quarterly study of digital music behaviors, reveal that in late 2003, more than one-fifth (21%) of American downloaders aged 12 and older had downloaded a full-length motion picture off of the Internet. Further, nearly one out of ten (9%) did so within the 30 days previous to the survey.