Minor update to the Retina MacBook Pro expected this week.
Apple Focusing on MobileMe Improvements in Latest 10.5.6 Builds
The latest Mac OS X 10.5.6 (9G35) build appears to focus heavily on testing of MobileMe syncing features for notebook computers in various scenarios. MobileMe is the online mail, calendar, contact and sync services available to Mac or PC users. MobileMe's initial rollout in July was marred by poor performance, downtime and some data loss.
Mac OS X 10.5.6 also incorporates the usual laundry list of big fixes and other tweaks to the 10.5 operating system. Apple release the last update to Mac OS X in September. There is no timeframe for 10.5.6's release, but it will be a free update to all Mac OS X 10.5 (Leopard) customers.