I jumped in twice today with my camera, off a jetty, whilst drysuit diving (Nikon D200 in a Sea & Sea housing with twin strobes) drop was approx 2m (OK, maybe 1.5) but the point was that an inflated BCD and flat fins meant that the housing didn't enter the water during the jump. Two hands needed to hold it above my head though!
If it's easy to get back to the jetty / hardboat / RIB, then having the camera handed down is first choice, but there are so many dives where either the conditions / current means "go - gone", or there's nobody available to hand down the camera, that a practical means of entering the water with camera is pretty high on the "needs" list.
I've jumped in / rolled off the rib with a Nikonos (IVa and V), various compact digitals, and now the DSLR. In every case the procedure is the same: use the diver's body to break the fall, and have the camera either not enter the water, or be tucked in close to the body. So far no floods!
Of course, the next dive may change my viewpoint somewhat, depending on the continued success, or not, of diver-camera entries...