While all three major news networks (Fox, MSNBC and CNN) saw a big decline in viewers from the 2009 inauguration, Fox's numbers literally fell off a cliff. (Via the Huff Post):
All three networks saw huge drops in viewership from the 2009 inauguration, as noted by The New York Times. Fox News was down the most, with a 75% drop-off from 5.291 million total viewers for the oath and the speech in 2009. CNN was down 61%, compared to 8.119 million total viewers. MSNBC saw a drop-off of 25%.
It's not exactly clear what this means - if Romney had been inaugurated numbers of the major networks could well have been reversed. Regardless, the less people who watch Fox the better, and this (hopefully) could be a sign of things to come. CNN is still struggling in the ratings war, but MSNBC is steadily gaining ground on Murdoch's network. Fox still dominates, but it is seeing a decline in its key demographic - not a good sign for the future.