Unless you are getting a lower interest rate, refinancing your home may cost you more money in the long run and may require you to pay higher monthly payments.
If there is a big difference between the initial interest rate and the APR listed in the ad, it may mean that there are high fees associated with the loan.
Resist "no cost" refinancing. No cost doesn't mean free. On the contrary: The closing costs are usually bundled into the new mortgage, which means you pay interest on them. The fees associated with a 30-year mortgage could cost you more than double what they would have had you simply written a check for them at closing. Or, if the costs aren't bundled in, you'll be charged a slightly higher interest rate. Either way, the lender wins.
If your new mortgage rate seems too good to be true then it probably is. Check for hidden fees in your mortgage that will make up that suspicious difference.