I've been seeing a lot of ads for a "DiCAPac" underwater housing. It's basically a robust waterproof plastic bag with a window for the lens to look through. It also has a few places for your fingers to reach into the bag to work the controls. Just search for it on Google or eBay and you'll find dozens of them. Does anybody have any experience with this item? How does it compare to a full ($$) underwater housing? I realize that this bag can't go as deep as the fancier housings.