I am sporting the white LifeProof. I've had this case since they started shipping, roughly July of 2011, and I had my iPhone 4 in it until I got my 4S.
The first thing you'll notice about it is that it is tall and wide. (pictures taken with an Atrix...I know, boo on me, but fresh outta iPhones when I'm showing both of mine side by side)
It does add thickness, but not as much as my old Otterbox Defender. (this pic also taken with an Atrix)
It has a slightly translucent white face, which makes it make any iPhone appear to be white while it's in the case. (all the following pics are taken with my iPhone 4 unless otherwise noted)
You can see in those two pictures where the iPhone ends (a millimeter or two between the grey LifeProof border and where the face of the iPhone starts).
The camera and flash have ample openings, but not excessively big like the Otterbox.
The tallness and wideness may give you trouble if you try to use it one handed and you don't have gigantic manhands like me. Especially when trying to reach notification center.
There is an issue with some of these cases (most notably the first generation ones) that you get what is called Newton's rings. This happens when the front cover is not perfectly flush with the screen, and light bounces out of it in a weird way. It bugs some people. It used to bug me, but I got over it. LifeProof will probably not replace it for that reason anyway.
There is a headphone jack cover that screws in.
They should have made the opening wider, though, because without their special $20 "adapter", the only cable that fits inside the plug when this cover is removed is the one on the earbuds that came with the iPhone.
The dock port, as previously mentioned, only fits the iPhone cable. Of course, they will also sell you yet another $20 "adapter" to allow you to use your phone with other cables or docks.
That and the small headphone jack opening seems like the only weak points of the case. They do recommend that you do not make a habit of taking your phone out of the case, as the case clips and waterproofness will wear out. It is rated for opening only 50 times. Luckily, the dock cover is rated for something ridiculous like 10,000 times or whatever.
I have taken the case swimming while my 4 was in it. Canoeing, too. Haven't had occasion to take the 4S swimming yet, but it is often taking a shower with me.
There is some slight, and I do mean very slight, discoloration of the grey border, I believe caused by the water in the river in which I was swimming & canoeing. You can see it mainly on the face of the buttons, but the effect is highly exaggerated in the photo. It still looks fine and grey to the naked eye.
Last but not least, I have not noticed any problems with picture quality or flash degradation while the phone is in the LifeProof. Picture taken by the 4S:
By the way, people unhappy regarding the Otterbox Defender's top flap: the hole is designed for the iPhone's noise cancellation mic, NOT the headphone jack. You are supposed to remove the flap to plug in headphones.