Not necessarily. I have 15K credit card debt at less than 6% until the loan is paid off. The trick is to max out a credit card, make a big payment, and then they send you a blank check for some ridiculously low rate for an indefinite period on your account with a note that says they hope they're not losing you as a customer. Then you pay the rest of the credit card off and write the check for (almost) your entire credit line. At least that's what Chase did for me.

I do have good credit, but then you have to have good credit to get a low enough interest rate on a mortgage to make it worthwhile, right?