A recent survey ranked YouTube number one when it came to online video sites. There was some pretty stiff competition too, especially from companies that might seem like they should have cornered this segment years ago, such as Time Warner/AOL:
"YouTube's share of the U.S. online video market was 60.2 percent in May, according to Hitwise. Its closest rival, News Corp.'s MySpace Videos site, had 16.08 percent of market share, the survey of Web surfing habits showed.
YouTube's sister site, Google Video, held 7.81 percent, while Yahoo Inc. had 2.77 percent and Microsoft Corp.'s MSN, 2.09 percent, according to the study."
The real interesting fact here is that if you added up the total visits to sites #2 through #65, you'd still only have about 2/3rds of the visits that YouTube garnered.