Another vote for the Sony RX100 - Definitely good enough quality that it is worth taking over a smart phone. Quite a bit better than the S90, which I had for a while. The high ISO noise of the RX100 is pretty similar to my old EOS-40D DSLR. At low ISO, resolution and dynamic range are actually noticably better. Handling isn't as good, but it's not bad for a compact, once you get used to it, and obviously there is more DOF due to sensor size.
If you're considering the Coolpix A, you should also take a look at the Ricoh GR when it comes out. Very similarly spec'd cameras with 28mm equiv lenses and 16mp APS-C sensors, and the list price of the Ricoh is $300 less. If I was going ultralight, I could see a place in the bag for both the RX-100, and the GR with the wide-angle adapter that gets it to 21mm.
I know many people scoff at Canon's G1X, but it's has very good IQ due to it's large sensor (almost APS-C size). But, although it takes good video, it's all auto. The nice thing is you wouldn't need any other lenses, has a high rez fully articulating screen and a (sucky) OVF in case you need it.
I hike and climb with a D600, usually a general range zoom lens and one or two prime lenses, depending on distance and location. Never felt I would save much weight in the big picture by going with something smaller, as the whole point for me to go to these places is to take nice photos.
My body weight plus full pack weight compared to the savings by going with a light weight camera is less than 2% - not worth it to me.
