For somebody who follows TV ratings closely, I can say that Survivor is still doing great in that area, the only show nowadays that consistently cracks 20 million is American Idol. Shows considered a hit are showing decline every year, like CSI averaging around 17 million and Desperate Housewives and Greys Anatomy averaging around 16 million this year. Survivor got these sort of numbers as recent as Cook Isalnd (season 13) {compare that to the fact that Grey's and housewives are in their 4th season}.

Additionally, Survivor averaged around 13 million for its latest installement (Micronesia) , this is a number that NO new show was able to reach on any broadcast network this year.
So, Survivor still has strenght in it.