People familiar with the latest build, reportedly known as 10H531, said the lone issue is associated with VMware. Having it installed can cause USB devices to not work when the Mac is awoken from sleep mode.
Those same people said Apple has asked developers to focus on a few key areas for the latest beta, including iCal, Mail, USB Devices, QuickTime, Time Machine and 3D graphics. The delta update is said to be a 557MB download.
Mac OS X 10.6.4 was released in mid-June, packing fixes for trackpads on Apple's notebook computers, and also addressing issues with Adobe's Creative Suite 3. It also included Safari 5, Apple's latest Web browser.