I agree, I've had a few people worry me while doing shihonage in a way I thought would break my arm. But I don't consider that proper technique, and it's certainly not the way our instructor showed the technique. I have been sent flying from shihonage before, but I was not particularly worried as breakfalls are a standard part of our practice and the person sending me flying was experienced and knew how to not break my arm.
I haven't had any trouble receiving ikkyo but have had had a couple of ukes wince when I applied it, I sometimes forget not everybody has wide, flexible shoulders. But I still haven't seen an ikkyo that was dangerous from an injury point of view, and I haven't found speed in application to cause any problems for that technique.
I have often seen (and had it pointed out by my instructor) that ikkyo can turn into an arm bar but that is often beacuse uke gets tense and straigthens out his arm, making it rather easy to attack his elbow, this happens even more often in nikkyo with beginners.
Nick, I'm in complete agreement with that last post.
My friend ikkyo!