Many people are quick to say that certain exercises, like the behind-the-neck press, will cause injuries. Of course, anything can cause injuries, especially if you're doing anything worthwhile or rewarding. The trick is to make your body physically prepared to cope with the demands of training.
With the behind-the-neck overhead press, the risk simply comes down to your posture. Bad posture? It's not the best choice for you yet.
Thibs is on a mission. The angry Canadian wants to see the incidence of training stupidity decrease. Are you a "kitchen sink" trainer or coach? Have you misinterpreted the concept of overtraining? If so, duck!