MobileMe seems to be up and running, after what many think was a poor implementation, with the launch of both MobileMe and the iPhone. There were early reports of loss data on the iPhone and presumably their Mac.
This update will only appear in Software Update if you have a MobileMe account. The slightly less cryptic description:
The Mac OS X Update For MobileMe is recommended for users running Mac OS X Leopard 10.5.4 and includes general system fixes that enhance your Mac for MobileMe.
Update: Mac OS X 10.5.4 does not enjoy the same automatic instant push service that the iPhone or MobileMe does. At present only iSync’s 15 minute intervals or manual push is available, as reported by AppleInsider.
The reader comments point out that subscribed calendars do not get pushed. Hardly enterprise ready.