Apple begin sending invites to a special media event on October 20 to discuss the next version of OS X. Although the invite doesn't expressly say so, the event must be about 10.7. "Back to the Mac," the invite says, showing a lion peeking out of the Apple logo.
It won't be the first time Apple has given a sneak peek of its operating system long before it shipped. In 2008, Apple previewed Snow Leopard at WWDC about a year before it was released.