I always bring a waterproof iPhone case on vacations or if I plan on spending a decent amount of time by water. The biggest downside to some of the waterproof cases is that you usually need to completely remove the case to access some or all of the ports to charge, use headphones, etc. And sometimes the responsiveness of touching the screen sucks so bad that I get frustrated and just rip it off after a little while. Mophie managed to leave all the ports accessible, even the finger print scanner (which I haven't seen on a waterproof case before), and include their signature battery back up. Pretty bad ass if you ask me.

Interesting, Lifeproof (Otter Products, LLC) just released for pre-order their FRĒ Power, a similar waterproof + power case. 2600mAh

I don't recommend. I bought this case, and the touchscreen (even with the double screen protectors) isn't good at all. First case I got leaked water, and so did the second one. Granted, it wasn't flooding, but even drops can ruin a phone if they go into the right place. If they fixed the leakage and touchscreen issue, I'd buy a new one.