I have heard that the one of the most common injuries in Aikido is a broken collar bone. If a front roll is not properly executed, the impact shock will travel to the collar bone area and result in a break. I have seen a couple of these. Not pretty. The mat does sting.
Interesting, do you think this gives any insight into the effects of Aikido used in self-defence against an untrained opponent?
For myself I have had no major injury yet in AJJ, thankfully. The worst injury I've sustained was tearing the ligaments in my right knee at a Judo contest when I was a teenager.