About two months after I bought the sd500, I picked up the WP-DC70. That’s the camera’s waterproof case (and well worn, as you can see). I personally grabbed it for snorkeling on the rare vacations, but quickly found it indispensable for the beach, pool, and most anywhere with dust or other contaminants.
You do have to be careful about the glass in front of the lens. Many of my beach shots have a bit of a soft-focus touch to them, or blurry spots. This is either water droplets that haven’t come off or my 4-year-old’s fingerprints.
The main thing, for me, is that it’s good to 120 ft (30 meters, really). See, just in case I ever go SCUBA diving, I want it with me. Proof of concept: in late February/early March I did exactly that, going down to 70 meters at the deepest. The two-year-old poorly maintained case still held up spectacularly.