40 yr mortgage?

Are you referring to a 40-year term, or a 30-year term balloon mortage with a 40-year amortization schedule? Either way, the attraction is a lower monthly payment than a fully-amortizing 30-year fixed loan. In theory, this type of vehicle enables the buyer to afford a nicer house. In practice, the ready availability of this type of financing just made the same house more expensive, so the same buyer got the same house with the same payment, but more debt. (Bubble, bubble...)

For all practical purposes, you can think of 40-year loans as IOs (interest-only mortgages). I think the qualification criteria have been a little easier, but there's very little real difference.

"More expensive" in the post above refers to higher purchase price, but with the same monthly payment.

One of my least favorite loan programs (which I hope is now deceased) was a 30-year balloon LIBOR ARM with a high cap and a floor equal to the origination rate. Heads they win, tails you lose.