I find the customer photos to be a fair representation of the RX100's capabilities -- what it can do in particular.
A few comments about this:
-Image quality is stunning, especially for a sub $1000 compact camera.
-Camera is lightning fast.
-I use the RX100 as my primary low light and events camera, as well as for snapshots, architecture/interiors, and as a camera to have on my person at all times. Image quality is great up to 800 ISO (and probably beyond).
-You can turn off the "Audio signals" on screen 2 of the custom menu -- this allows you to off auto focus and shutter noise. My RX100 is completely silent in use.
As for what the camera can't do, actually, I would say more like what I do not use it for:
-You can use the RX100 for landscapes, but I prefer an ultra wide zoom on my Panasonic G3.
-You can use the RX100 for portraits, but I prefer using the G3 with fast primes.
Thus, what the camera "can't do" or "isn't best at" (for me) -- the wide end of the zoom is 28mm (I prefer wider angles for my 'scapes), and the long end of the zoom is not so fast, at f4.9 maximum aperture (I prefer fast primes at these focal lengths).
In summ, the Sony RX100 is a perfect fit, a no-brainer, for my two-camera setup. If you only plan to own one camera, I think the decision comes down to your image quality/sensor size needs, and your lens needs, vis à vis the compromises involved in trying to fit so much into such a small package that you can carry it with you everywhere.
Terrific answer, and thank you. That helps a lot. I am looking for a second camera-- a travel pocket camera to compliment my beast of a DSLR. I also pack the 2d camera in my cycling jersey on rides. I currently have a G11 that is long in the tooth, so am looking at both the Sony and the G15. Your comments are quite useful, and while I am waiting for the reviews on the G15, you have me leaning back toward the Sony.