From what I understand, it's basically like a cash out refinance I talk about in real estate investing thread. You get a loan using an asset as collateral. Loans aren't income so there is no income tax. You still keep your asset, so future gains are realized, less the cost of money you borrowed. I'm a fan, but it comes with risk relative to the amount you own and the amount you borrowed.
It's not rocket surgery, but it's a powerful tool.