In this version the developers are asked by Apple to test certain areas like Safari, Mail, Adress Book, iCal and Spotlight according trusted report.
And it is also said this update is Apple's next free maintenance update for OS X Lion users. And the previous version which is OS X 10.7.2 was launched in the last October last year to gave iCloud services support.
And this new Build 11D42 is allegedly will deal with new graphics cards for the Mac Pro update and added HiDPI display modes to bring a Retina display on MacBook Pro, that is firstly rumored by DigiTimes.
MacRumors's update post says that this version is likely the golden master version of OS X 10.7.3 and it is suspected will get to public pretty soon. As the result we can expect a public release of this build in the relatively near future.