I dove with Top Dive in Bora Bora and they were a top notch dive op. No overcrowding, attentive DG's, emphasis on safety, great boat, and great sites. We didn't do a shark feeding dive.
In Moorea also with Top Dive, with similar quality boat, staff, and sites, we did do a shark chumming/feeding dive, although I didn't know until just before the dive. They asked if we wanted to see a shark feeding, and since I hadn't done it yet (2007), I said ok.
They made it very clear that we were to stay behind a ledge, our hands were to stay under our armpits or close to our body if photographing, our fins were to stay down, and we were to stay put. They ensured that everyone was in position before one of the DG's trailed a fish head in a cage and hid it under some rocks. Within 10 seconds, some lemon sharks circled the rocks and then a 9 foot or so grey shark came in, and the lemons took off. The grey shark got it's nose under the rocks and got the fish head and ate it or parts of it, then it left. The lemon sharks came back briefly, scavenged around, and left. The DG went over to where the fish head was, and picked up a shark tooth and gave it to me.
I also have to say that in French Polynesia, sharks are abundant, and certainly no chumming is required. We saw tonnes of greys, lemons, and black tips throughout FP, especially in Raiatea.