Meet YouPorn: The X-Rated YouTube

Google's (GOOG) YouTube is the runaway winner in the general-purpose Web video sharing market: In March, it received 73% of all U.S. visits to video sites, according to Hitwise.

Our question: Who's the YouTube of porn?

Trusty ComScore (SCOR) doesn't release metrics for adult sites, so we ran five big sites through Compete instead. Results: YouPorn (biggest audience) and RedTube (fastest growing) have jumped ahead of the competition.

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