Very very common. Especially after that Navy Diver got attached several years ago in Rose Bay. I have a mate that told me some interesting stories after this attacked and the DPI started tagging them. On their first few tagging outings, they were severly undergunned with hooks being bend, reels breaking under pressure, and line breakages.
I was a North Head years ago when a member of this forum had a big Bull shark grab his kingy boat side, it was a big bull as it dragged his boat off anchor for a couple hundred metres before he was bitten off.
Dan