[Jonny250]

I have a G9 with Canon Housing; remember that the canon housing does not allow you to change the speed, apature or custom setting once the camera is inside the housing. I find this to be a major limitation when taking images at different distances from the camera (amount of background illumination), ok for macro tho.
Also consider getting adequate lead to hold the camera down - way too buoyant otherwise - unless you're attaching it to a gun.
personally, i am looking to use a tripod for longer macro work (50cm) - the camera can take half a second to find the focus which can make a significant difference when floating around..