Sorry for the double post (I originally posted this on the accessories board, but figured people looking for a review would look here)....
I just used my new Guardian for a week in the Caribbean and I figured I'd give everyone a full report:
I loved, loved, LOVED this case. I spent 7 days sitting either in the Caribbean Sea or the swimming pool, reading my K2. Not once did a drop of water or grain of sand get into the case. You can truly submerge it and it floats back to the top of the water!
Okay, lets answer some of the questions people seem to have about the case:
Power switch -- Yes, it is kind of annoying that you can't access it without opening the case. But the Kindle stays awake for a long enough time that it wasn't a huge deal. Even when I fell asleep and would need to turn it back on, I was able to open the case on the beach (with the strong tradewinds blowing) without getting any sand in the case.
Accessing the controls through the silicon -- Totally easy, I've seen some people say it is difficult to use the joystick, but it just takes a little practice. The Next page/Previous page/Menu buttons are very accessable and easy to use.
Reading through the cover -- There's NO glare, which was awesome. I sat in direct sunlight for most of the week and had no problems reading.
Couple of things to remember -- 1)Follow the directions that come with the case and test the seal before putting your Kindle in it. 2)The case will fog up a bit if you go from very cold air conditioning to hot, muggy air. It will burn off quickly if left alone.
Here's what "Carrie" looked like in her Guardian on the beach:

And at the pool:

Let me know if you have any questions!