Preview at WWDC likely in June, followed by September launch.
Apple Already Working on Mac OS X 10.7 Development
< rdar://problem/7386864> 11A47: SecurityAgent no longer visible via AccessibilityApple's build numbering scheme utilizes a numerical prefix indicating the major release version, followed by a letter code indicating the minor release version and a numerical suffix indicating iterations of that version throughout its development. For example, the initial shipping version of Mac OS X Snow Leopard was termed Build 10A432 while the 10.6.1 update carried a designation of Build 10B504 and the 10.6.2 update released last week was termed Build 10C540. Meanwhile, Mac OS X 10.5 (Leopard) carried a build number of 9A571 when it first launched.
Based on this numbering scheme, the "11A47" entry cited in the launchd change database would refer to the initial version of Mac OS X 10.7, with the "47" suffix indicating that, while still early in the development process, Apple has been working on builds of the next major operating system revision for at least the last month or two.
Of course, news that Apple appears to be working on Mac OS X 10.7 is certainly not surprising given the long development time required to refine and polish Apple's major operating system releases. While 10.6 incorporated many "under the hood" changes, however, some have speculated that we may see more radical end-user changes in 10.7.