An evaluation of the latest Mac OS X 10.5 build provided to developers reveals steady progress has been made with the operating system in the past number of months, but significant stability issues persist, all but arresting any hopes for an early release at or around Macworld Expo San Francisco next month.

The new build, 9A321, is the first to feature an updated installer as well as images during the installation process touting Leopard’s new features. Help files and other documentation have yet to be updated to reflect new changes in Mac OS X 10.5.

New to build 9A321 is support for Sun’s ZFS file system, a 128-bit open source file system introduced with Solaris 10 that offers support for vastly larger drives and arrays than 64-bit file systems. Think Secret has put up some screenshots of the new Mac OS X 10.5.