According to John Gruber, there will be no beta of Mac OS X 10.7 to developers attending WWDC this year; the firm prefers to concentrate on iPhone OS 4.

OS 4 A WWDC focusing on iPhone OS 4
He most likely waits for the WWDC next year before we hear officially about the new version of OS for Macs. According to the developer, the reason for this delay is simple: Apple has reduced the teams working on the project. If the development of the OS continues, schedules were rearranged to face the emergence of Android and the competitive market of smartphones.
Snow Leopard is maintained very well against the competition and Mac sales are at their highest. We also remember that it was not until more than two months between the release of Mac OS X 10.5 and 10.6 which has not brought great revolution. For comparison closer to what Mac OS X 10.7 is supposed to note it was not until 30 months between Tiger (Mac OS X 10.4) and Leopard (Mac OS X 10.5). In short, following the last logical, it would not be surprising to see a new version of the operating system released in 2012 with a beta introduced in 2011.