Ok, let's expand on this. To simply say that this is a dangerous loan product is not fair. The danger is not the product itself, it's in the lack of understanding of how the product works. Lack of understanding and a lack of financial planning for the future (and the natural decline of the housing markets) is what has led to the current level of foreclosures around the country today.
The Pay Option Arm, like Ryan stated, is an adjustable rate mortgage with a variety of payment options (in most case 3).
Option #1 is the full principal and interest payment (same as a 15 or 30 year fixed).
Option #2 is the fully indexed Interest only payment, where you are simply paying the interest generated that month for the loan (same as an Interest only Mortgage).
Option #3 is the minmal Interest payment (at a rate of around 1% to 3%).
For many home owners, how this third option works was either never explained to them or they chose to ignore it. The minmal interest payment option works like this:
EXAMPLE
Let's take the $250,000 mortgage that Steve brought up earlier. Let's say he's using a Pay Option Arm at 7.5% interest. His payment choices would look like this:
Choice #1 (full 30yr. P&I) = $1.748
Choice #2 (Interest Only) = $1,563
Choice #3 (minmal Interest at rate of 2.5%) = $521
Now here's the catch. Regardless of whether you pay the interest only of 7.5% or the minmal interest of 2.5%, the loan is still generating interest every month at the fully indexed rate (in this case 7.5%) Choice #3, the minmal interest payment, does not cover the interest generated for the month.
So in this example, where does the additional $1,042 in interest go? You guessed it, right back into the principal. This is why this payment option is referred to as negative amortization. The lender will allow this increase in pricipal to continue until you reach a cap of anywhere from 115% to 125% of the original loan amount. So on this $250,000 mortgage, the minmal payment option could be used for 35 to 59 months before the lender will stop allowing it to be used. The risk you run when using this option month after month is that sooner or later you are going to outpace to the market value of the property and become upside down in your loan.
Ryan is correct in that if you are purchasing a house at market value and you can't cash flow with an interest only payment, then yeah you're proabley better finding a new deal and not using the Pay Option Arm. However let's say that our $250,000 mortgage is 90% LTV and the house is actually worth $275,000. Assuming that your housing market isn't in a decline, then you can rent the house for 12 months, pay the minmal interest payment and have the increased cash flow and then sale the house after the 12 months and still clear about $12,000 (minus your cost to sale). I know investors here around Atlanta that have using this stragety for years. They use the increased cash flow to increase their reserves, make other investments, etc.
So yes this is one of the best tools you can use for positive cash flow, as long as you understand it and know how to use it. For rental properties, how much you can use the minmal monthly payment option without hurting yourself is directly linked to how much equity you have in the property when you buy it. The better your equity position, the longer you can rent it and make the minmal interest payment without outpacing the market value of the home.