I have heard that after 3 or 4 times of re-finance, no bank will lend you money for such low rate. So this approach will save you just one year's interest. If interest rate goes up-trend, you won't get the same low rate you could have locked one year ago.

If you happen to lose job before refinancing into a long term loan, you are dead. No bank will lend you money and you will be trapped in such program and suffer from the high interest rate after the seducing period ends.

Plus, frequent re-finance hurts your credit score a lot because every re-finance will pull your credit report and open a new account with the new bank. Too many credit inquires and too many newly opened accounts in short period of time will drag down your credit score a lot. If your credit score drops below 700, it's hard to get good interest rate when refinance.

Knowing all the hidden issues, if you still feel comfortable, go for it. But just get well prepared.