Looks like Facebook is the biggest challenger in the UGV space:
The number of online video streams viewed on social networking and blog sites increased 45 percent year-over-year, from 240.8 million streams in October 2008 to 349.5 million in October 2009.
During the last year, Facebook’s online video viewing audience has experienced tremendous growth. Year-over-year, total time spent viewing video on Facebook increased 1,840 percent, from 34.9 million minutes in October 2008 to 677.0 million in October 2009. The number of unique viewers of video increased 548 percent and total streams grew 987 percent during the same time period.
Source: The Nielsen Company 
