Apple has already begun work on the next major revision to Mac OS X which is being labeled as version 10.8



From MacRumors:

Apple only just released the final version of OS X 10.7 (Lion) to customers in July. OS X Lion was the first version of Mac OS X to be distributed through the Mac App Store and it included a number of new features for the Mac. These included an iOS-like application launch screen known as Launchpad, full-screen apps, a new combined interface for Dashboard, Expose, and Spaces known as Mission Control, enhanced Multi-Touch gestures, and improvements to a number of core applications such as Mail.

  Apple Has Already Started Work on Mac OS X 10.8