Chevrolet general manager Ed Pepers spoke up at the Chicago Auto Show and mentioned that the brand is looking at adding a model with "more horsepower" than the current Z06-- noting the current über-Vette's popularity, and subsequent difficulty of keeping them in stock (presumably, GM would like more problems of this sort).
This could be taken as an acknowledgement that there's more to be had from the current Z06, but there's enough paperwork floating around sites like DigitalCorvette.com about an "LS9" that it's almost impossible at this point to deny that the Blue Devil (or whatever you want to call it) program exists at some level. The latest rumor is that the LS9 might be a DOHC design. Of course, that might just be a typo on a data transfer request (other documents seem to clearly indicate that the LS9 will be supercharged).
Regardless of how this new engine breathes, GM has clearly not been sitting on its ass with regards to the last two generations of Corvette, and as such, we fully expect something faster to come along in a few more years. Until that happen... we'll continue to enjoy the speculation.
[A tip o' the hat goes out to Keith at CorvetteBlogger.com]