Apple released an update to OS X 10.5 (Leopard) today. The standalone update is 110mb but when I downloaded it this morning through Software Update it was a 38mb download for my machine.
According to the Apple info page on the update, it:
includes general operating system fixes that enhance the stability, compatibility and security of your Mac
The page goes on to include details of fixes for Airport, Mail, iCal, System and Finder as well as other fixes.
Personally, I love Leopard. I know some people have had issues with it but I have had the opposite experience. The upgrade to Leopard has actually fixed two previous problems I was having with 10.4 and my laptop is now running faster too. Hopefully 10.5.1 will resolve most of the early issues people have had with Leopard.