From Ari's piece:
In very simplified terms the Nokia 808 PureView combines the information from roughly seven pixels and uses this info to re-create what we call super pixels. The benefit of doing this is that when you multiply several signals (or pixels in our case) with random noise floor, you end up with amplified signal, but lower noise floor compared to the actual image signal. The most obvious benefit from this is the improved signal-to-noise ratio in low light images, but also daylight images benefit from this as an increased dynamic range. And indeed the dynamic range of Nokia 808 PureView is huge and achieved without any additional HDR processing, which often may lead to unnatural results.
...Digital camera markets are currently full of all kind of HDR cameras and applications to handle those very high contrast scenes but with Nokia 808 PureView we took another route. We actually designed and executed a camera that is simply so good, that no extra HDR processing is needed.
Interestingly, Ari also highlights the live exposure histogram that appears automatically when you opt to adjust exposure:
Also very welcome feature for more serious photographers is the live histogram that makes achieving the perfect exposure very easy. Just adjust the exposure compensation so that the bright part of the histogram does not clip, and the massive dynamic range of the Nokia 808 PureView will preserve the details in the dark end. As you can see from the image below, the live histogram becomes visible automatically when exposure compensation is adjusted.