The using of the manual focus is good to navigate in the menus only. You cannot use it in other situations, e.g. in manual mode you cannot change the shutter speed since it controlled by the up/down options.
(It can be solved by moving to Tv option set the shutter speed and then return to manual)
Not correct. You can control everything just like without using the waterproof case but only valid for S45/S50. You cannot change the APERTURE in Manual mode with waterproof case if the model is S40S30.
Refer to this URL:http://www.canon.co.jp/Imaging/PSS50/PSS50_3000-e.html for details.