Never heard of it before. But sounds exactly like a pyramid scheme to me.
Someone described it recently, but i'm not sure if it was here or not.
The basics being that a pyramid scheme has no product, they take money from person A, in 6 months they take money from person B and give persons A + a bit of B's money back, keeping the rest of B's money. They convince person A to reinvest over and over, in another 6 months they take person C's money to pay off person B, but again convince him to reinvest.
It eventually falls in on itself when not enough new people join, to pay off the existing 'investers'.
MLM has a product to sell.
Sell the product for x price to A B and C, tell them to each sell it onto 3 people for their own profit, telling those 3 to sell it on again.
In reality pretty much all sales are to these people trying to sell the product on, never to people who actually want the product.
That seemed to be the gist of it, because MLM has a product, it's legal. Pyramid schemes don't, they just straight take cash from people on the promise they'll get a high return.