Apple released the second developer preview of Lion—build 11A419—this week, but in contrast to rumors suggesting that a possible release candidate would appear soon, the latest build still has known issues and isn't fully stable. Sources tell Ars, however, that the build does include some major visual changes to iCal, a new About this Mac, and possibly a new default combined account list for iChat.

The most notable change is the continued iPadification of iCal in the latest Lion developer preview. The first preview revealed new views similar to those used in the Calendar on iPad and MobileMe, but Apple has now tweaked the window header to take on a stitched leather appearance. The typeface on the buttons and tab slider have also morphed from Mac OS X's default Lucida Grande to iOS's default, Helvetica. So far, the change seems to be getting mixed reactions—while some developers consider them garish, others feel they are a worthwhile deviation from Apple's own Human Interface Guidelines.

The About This Mac dialog has also gotten one of the most significant updates since Mac OS X first shipped in 2001. It now is divided into two sides—the left shows information about Mac OS X, while the right shows information about the Mac hardware. A button to check for software updates remains, while the "More Info" button has been replaced with the more descriptive "System Report." New tabs give quick access to information about attached displays, storage devices, and installed memory. Two buttons on the right offer shortcuts for Support and Service, which provide links to various resources on Apple's website.

Finally, 9to5 Mac reports that iChat has gained the ability to consolidate buddy lists for various chat accounts into a single, unified view, similar to Adium. However, one developer told Ars that this ability existed as a preference in the first Lion preview. It may be that the unified buddy list is now the default option.

Mac OS X Lion is slated for a summer release, and further details are expected to be revealed to the public during Apple's Worldwide Developers Conference in early June.

UPDATE: One of our sources told us that the original small "About This Mac" dialog still comes up when selecting the option from the Apple menu, and that the new box appears when clicking "More Info." Previously that button would launch System Profiler. Having both boxes seems redundant to us, however, and we'd like to see it replace the old box entirely.

Furthermore, our friends at OSXDaily noted that this new box was also present in the first developer preview. Our source hadn't seen it before and we hadn't come across it in previous coverage, hence our assumption it was new to the second Lion preview.