Apple released 10.5.8 this week offering several bug fixes and application updates. Safari is now at version 4.02, which improves the accuracy of a full history search. Bluetooth reliability, iCal reliability, and many more. It also includes the latest security and bug fixes.
Get the full details from Apple
As always, you can get the smaller delta update via Software Update, but it's been my experience you will have a much smoother experience with less problems if you download the 759MB Combo updater. The downside to this is that is always much bigger, but if you have Broadband internet, it shouldn't be much difference.