The safe areas vary from television to television. They also vary with the age of the television (the picture tends to shrink as the tube gets older, hence the whole reason for having an overscan area to begin with), with how long the TV has been on, the temperature, how close your stereo's speakers are to the TV, the brightness of the image, and probably is also dependant on the phases of the moon, the brand of toothpaste you use, and what your cat found under a rock and ate last night. (OK, so i'm slightly kidding on those last three, but only slightly ...)

My advice is to make sure anything vitally important is within the minimum safe area, and make sure that anything outside the safe area is still something you wouldn't mind having people see.