MediaPost reports that among a group of 58 of the leading social networks, MySpace.com received 72.73% of the market share of U.S. visits in May, according to new data from Hitwise.

Interestingly, the overall market share of U.S. visits to Hitwise's social networking category decreased by 1% in May compared to April, and has decreased 6% year-over-year. Facebook ranked second at 16%, while everything else scored about 1% or less in the survey.

This is what you would call a huge head start, when it comes to consumer brand recognition on mobile as well—which explains why MySpace and Facebook also lead mobile social networking sites.