The ratings for Nick definitely took a plummet. But that's mainly because almost all the shows are bad now - even iCarly and Spongebob have significantly decreased in quality. All the new shows are complete ****, and what not. Victorious is still a good show but like Good Luck Charlie & Phineas & Ferb on Disney Channel, it's not enough for someone to watch that channel.
Nick at Nite isn't as fun either - Friends is awesome, and I actually am really addicted to Hollywood Heights - Cody Longo and Grayson McCough

but the other shows aren't that special - Yes, Dear, George Lopez, & My Wife & Kids are forgettable.
That's mainly why ratings have been plummeting like hell. I mean, even the one hour specials aren't getting good ratings anymore. I was shocked to find out Tori Goes Platinum only had a 3.8 rating.
But, still, ****** ratings is no excuse for Viacom to demand more money. It's not gonna help. The ratings are gonna fall even more because of this.