I would imagine if you were the only person in your neighborhood downloading a movie you'd be OK, timewise. As done with other types of media a portion of the content is downloaded and a continuous stream is fed to the backend so one doesn't have to wait for the entire download.
However, if this takes off I can't see how cable, satellite and DSL networks wont get saturated. Especially during peak viewing times.
http://news.yahoo.com/news?tmpl=story&u=/nm/20040907/wr_nm/tech_netflix_tivo_dc_4