I tested this with my own iphone and luckily it didn't leak!
As a case it isn't too big and bulky, both the camera's are useable, as well as the touch screen (although a little extra pressure is needed). I don't think the touch screen works under water most likely due to pressure, not a big deal though. It would definately protect against a drop of a couple of feet as the rubber is pretty thick, althought I'm not going to test that.
I am wondering how long the rubber case will last, the main two problems that could arise would be for it to discolour and effect the camera. The other would be how long the seal lasts. Obvioulsy cleaning rubber isn't that easy once its grubby. I found by using one of those shamy cloths for swimmers left a lot less fluff on the rubber.