I have used them for years and always taught them with no problems. I have only seen beginners with low levels of flexibility as even representing a potential for injury.
However, a number of athletic trainers are recommending against both. However, I have seen no research concerning a direct relationship between the performance of these stretches and injuries.
Again, I see the risk in very inflexible and out of shape beginners, but generally speaking, is this an old wives tale?