a few months ago I saw hundreds of wedding pics shot with a D700, the photographer was a pro working for Cosmopolitan, her assistent too had a D700, both relied on high ISO even for indoor shots, no flash-
must say techically the pics were rather awful !
when you have no light, your pics will lack detail, will lack color, no matter how high-ISO capable your camera is !
dynamic range was very insufficient too, the brides gown had blown highlights all over, on close inspection images looked noisy, even at ISO 1600 !
while for photojournalists it is convenient to shoot discretely without flash, flash shouldn't be dismissed altogether-
at a wedding party dozens of amateurs use their p&s with flash anyway, so should the pro !
images I saw shot on the same day with an amateur D3000 (using the built-in flash) looked clearly better than the pro's !!!