I haven't been on a dive that was specific to diving with sharks, but anytime you get in the ocean there is a possibility you'll run into them. I've seen white tip reef sharks in Hawaii on two out of three of my two tank dives when I was out there. They are pretty docile and apparently not that common, even though we saw at almost one each dive trip. My favorite so far has been diving off Jupiter, FL and seeing two lemon sharks. One had a hook and fishing line hanging from its mouth. I wanted to help it but he was cruise'n and wasn't planning on hanging around us. Right after seeing those two we saw a huge Goliath Grouper. here's my pics of the shark and the grouper in the distance, and another pic of the grouper much closer... the grouper was bigger than my 6'5" husband.
(the picture does not do the grouper justice)