The most common are broken noses and ribs. We do, however, have an occasional broken hand or arm. We have even had a couple of ACL tears during testing. Yes, they are most common during the sparring portion, but there has been a few that had cracked ribs during Niseishi testing(very similar to Sanchin testing) from the use of a shinai. This is common in the Chito-ryu school, not very common in the TKD school. The TKD school has mostly bruises and a few cuts. TKD is not quite as brutal, as far as injuries go. I actually go to the "brutal" school just for some training and for tests. I have tried to keep injuries to a minimum at my own school. I do have those 18-36 YO guys that always want to try and kill each other, but they are all a bunch of freaks.
Hope this answers your question.