I have two Aquapac's, neither seem to be sold on the website anymore so I can't link them.. but they both work quite well, they're very durable, waterproof, float if dropped. They will NOT protect against falls.
The biggest problems I've had with them in the past was if you have a rubbery case on your phone, the case can either stick to it or be difficult to get in or out of the pouch. Previous phones I had Best Skins Ever on and they stick to those types of phone skins really hard, in fact I used to keep a small piece of wax paper in the case. But if you don't have that type of skin on your phone, it's no problem.
Operation is just fine, only problem I have is when it's raining and the case gets rain droplets on it the screen sometimes acts funny.. Usually I hit the power button (suspend), wipe it off, turn back on and it's fine. Don't know that salt water would be any worse offhand, but just fresh around here. And they are built really well, the seal and mechanism you know it's closed.
If you want something that's waterproof AND pretty much damage proof, get an Otterbox. But you won't be able to use the screen. I'm planning on mounting an Otterbox 2000 on a 4-hole GPS mount that'll mount on bike handlebars for biking with the phone accessible. Some foam and it should be good for vibration, water, and the potential fall (singletrack, not bombing down mountains but still rough stuff).
