Are we like not even allowed to talk about renting out our home in order to upgrade or something? That's the play right now. Net present value of your almostfree money is maximized by turning it into cashflow. Plus you don't blow 6% on closing costs, and it's all the same to the bank in terms of getting another loan. It actually ends up being an equity asset as well as income.
Err, what I meant to say was murder all landlords.
It's possible, if you have the savings for a second down payment. I'm pretty sure you also lose certain tax advantages if you convert your primary home to an income property. Depending on how long you've owned it, that can work out to a serious hit.
You can't deduct the mortgage interest (you can on the new primary residence though), but suddenly every dollar you spend on the rental property is tax deductible as a business expense. And you can like deduct depreciation on the appliances and shit. It's actually more tax advantaged in some situations.