You may want to amend that to a third of net income. Even so, many people followed that rule and lost in the housing market. Your experts will be issuing revisions soon I'm sure.
How would you lose if you followed that rule?
1. You used an ARM to achieve the payment.
2. The martgage balance is higher than the home's value.
3. You lose your job and can't find one at the same rate of pay.
Only #3 would technically be correct.