While not nearly as interesting as the impending Q1 release of Snow Leopard, Apple has today started pushing a fairly hefty update to all plain old Leopard users.
Version 10.5.6 is the fella in question and though rather drably described as "recommended for all users running Mac OS X Leopard and includes general operating system fixes that enhance the stability, compatibility and security of your Mac" - it has some mildly interesting bits and pieces.
Keymost in the near 400MB download (though it is weighing in at between almost 700MB and under 200MB for some users) is better reliability of AirPort connections, iPhone MobileMe syncing inside one minute when a change is made on your Mac and improved Apple File Service performance. General speed tweaks are in there too along with better Time Machine reliability with Time Capsule, fixes for occasional ATI graphics card based glitches and a rather overdue spit and polish of Chess!
Should you wish to wade your way through the full list of minutiae then check out the link below. For everyone else just sit back and let it do its thing, an approach I'd say is probably for the best - both mentally and socially...
Manual Download Page (if necessary)