Lacey Rose has a great article on Forbes that looks at what Mad Men means to AMC:
What's more, the heavily hyped series from The Sopranos writer-producer Matthew Weiner, which HBO, Showtime and others famously passed on, has redefined its formerly moribund host network. Once just another movie channel, AMC is now the buzz-worthy home of critically acclaimed and Emmy-winning fare like Mad Men, follow-up Breaking Bad and the upcoming mini-series remake of The Prisoner. (Though AMC's movies fail to generate the same level of awards or press, they remain an important revenue stream for the network.)
The article also has a bunch of numbers in it, and notes that Mad Men has more adult viewers aged 25-54 with household income greater than $100,000 of any show on cable.