Although Apple's new Snow Leopard operating system is in the pipeline, and coming up for a release sometime this year, work it still being continued on their current operating system, Leopard.
As AppleInsider reports, on Thursday, Apple made a new build (codenamed "Juno") of Leopard's 10.5.7 available to developers, bringing with it over 80 bug fixes and updates. Those who have had some hands on time with the build (number 9J30) have said it includes an updated Flash Player, as well as 5 other bug fixes, bringing the grand total in the 10.5.7 update to over 80, as mentioned.
Apple has also fixed security and cookie issues with Safari, as well as concentrating on iChat, iCal, the CoreGraphics framework and the HFS+ file system. These fixes aim to please, as I myself have had cookie issues with Safari, and it should provide a suitable update whilst Snow Leopard finishes development.
It is expected that more pre-release builds of this update will be sent to developers in the near future, so it's unsure how far away 10.5.7 is from public availability.