A lot of these digital cameras (and point-and-shoot film cameras too for that matter) have the shutter and the apature working together as one part, so the f-stop doesn't function quite like a 'normal' lens. It all depends on the camera and the exact design. With some cameras you don't get any DOF control, and with others you almost get what a normal lens would give. Also, that's why you don't have a full selection of shutter speeds at wide open apatures. The circular shutter is built into the apature diaphram and it can't move that fast. For example my G2 is limited to 1/640 sec. until the lens is stopped down to f 5.6, then the speed increases on a sliding scale, reaching 1/1000 at f 8.
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