It's called 500 Person Sex and it's apparently the human porn version of March of the Penguins.
"Imagine going into a large room and seeing 500 people giving oral sex and screwing their brains out. What better way to start the summer? … 250 girls and 250 guys go at it together in a large warehouse. Every sexual action is in sync, so be prepared to fall off your chair from this crazy feature. Japanese amateur lovers will definately be delighted with this video." -EthnoroticaThe things people feel the need to tell me about (and I feel the need to pass on to you)!
WARNING: All links NSFW
EDIT: Video clip