I am using the Ultima Digital underwater housing for the Hasselblad line of digital cameras which is large , but smaller than the old 6 X 7 housing which I also had some experence with. I have also used the Nauticam housing for the current PhaseOne digitals. Both housings are a bear out of the water and can be used with one hand underwater. Most of my images have been taken with the wide 28 mm lenses and the Hassy 120 macro.
I hope to see some housing maker stepup and design a Pentax 645D. I am still holding the 120 AF 645 lens and would love to be able to shoot the new 25 F/4 lens.
These are great systems for U/W photography if you need the upsides of giant file sizes and fashion shoots in the pool are growing as an art medium.
Hasselblad Underwater Fashion Workshop
Phil Rudin