I had this exact problem. It was only on my passenger door, and over the first three months of ownership/2,000 miles I had squeeze harder and harder to get the door to release. Actually it was usually a friend or my wife trying to get out, and they kept thinking it was locked.
Anyway, when I went in for my first service I had them adjust the door, both the release handle and the frame/striker area. It was very quick (they also adjusted my driver's door slightly and changed the oil -- all in about three hours) and it's been fine ever since. All free of charge of course (even the oil change, because the first one is free at Santa Monica Ford if you bought your car there). :thumbsup