Most folks following the industry know that YouTube is the most popular online video site, but it's a bit shocking to find out just how much. MediaPost is reporting that YouTube accounted for 75.43% of all U.S. visits in May 2008, according to new data from Hitwise. "Among a custom category of 63 online video websites, MySpaceTV received the second highest percentage of visits with 9.01%, followed by Google Video with 3.73%."

(YouTube is available on mobile via various carrier-and-WAP initiatives, but MySpaceTV so far isn't.)

To put the new numbers in perspective, the report said that online video accounted for just 1.14% of all U.S. Internet hits in May 2008, which is actually a slight decline from the year-ago period. However, people spent slightly more time on those online video sites than before.