For those curious about this camera's sensor and other technologies, see
http://www.lsst.org/lsst/science/concept_cameraAs usual with astronomical cameras, it uses CCD's: lots of 40x40mm ones butted together, with 10 micron pixel pitch. The butting gaps are only promised to be "sub-millimeter", so there will be very visible join lines that would be unacceptable for "artistic" photography.
But what about the worse noise floor of CCD's compared to modern CMOS sensors?
The focal plane array operates at a temperature of approximately -100°C to achieve desired detector performance. The focal plane array is contained within an evacuated cryostat, which incorporates detector front-end electronics and thermal control.
So it sounds like both sensor dark current noise and thermal noise in the analog electronic signal path are controlled in a way that us "hand-holdable camera" photographers can only dream of.
Also, fulfilling the dreams of many forum commentators, the sensor is circular! Or rather, the 189 individual square sensors are arranged to cover the image circle of the telescope, with minimal overhang.