"Sci-fi/fantasy — particularly fantasy — has been trending mainstream for a decade now...
...though one could easily make the argument that there were other decades in the 20th century where it was so mainstream it didn't have its own section in the bookstore. All I know is, when I was growing up in the 80's and 90's, if you read Lord of the Rings, you were a nerd. Nowadays you barely qualify unless you name your third external hard drive after a Silmarillion character. So, no weeping about the state of sci-fi/fantasy from me.
"The market is very tight in this genre, and always has been. There's some argument that it's gotten too conventional. My agent shopped a post-Apocalyptic novel to sci-fi publishers last spring and it didn't sell. We got some very nice letters back about how it was very wild, interesting, etc, but they weren't sure 'how it would do in the market.' In other words, 'We can't predict whether it will sell and therefore can't invest the money in a new author with a risky book; go write a vampire story.'"
— The Rejecter, an anonymous assistant to a literary agent, blogs about the state of the SF/F publishing market