Tax-exempt securities

My wife and I are in our early 60s, with a son in college. We have Roths and 401(k)s. I will get a pension from the state of North Carolina when I retire in a few years -- not so for my wife. What I need to know is: Is there a reason not to put so much of our savings in munis? (I would take the money out of some of our mutual funds.) I would not get munis from states with problematic economies; I would most likely get them from N.C. Also, what is the best way to purchase tax-free munis? Thanks! Stephen, Durham, NC