Up until now 10.3.6 has been probably the best overall version of OS X. I'm on 10.3.8 w/ my G3 dual USB iBook and I don't have enough problems to drop back, but people happy on 10.3.6 probably shouldn't update.
I'm hoping 10.3.9 will be a good end point for my iBook, however. Below is the AppleInsider description.
In a seed note accompanying the latest build, Apple reportedly told developers to focus their testing efforts in the following areas: Bluetooth, DVD Player, FireWire devices, Modems (both internal and external), Networking, Printing, Safari, Terminal and USB devices. The company also asked that developers assess the 'general system usability and reliability.'Note the change in kernel - presumably from a 7.8.x version to 7.90. Superstition has it that changes on the second digit are big. My hunch has been that some of the SMB share and firewire problems need to be addressed very deep in the OS -- maybe this is where that will happen. I'd figured Apple wouldn't mess with the deep insides until 10.4.
Apple also listed approximately 30 areas of change and enhancement that are already reflected in build 7W72. Some of these improvements include various video driver fixes, improved Directory Services performance, Java garbage collection optimization, 'wake from sleep' performance improvements, and a new version of the Mac OS X kernel (7.9.0).
Mac OS X 10.3.9 will also usher in bug fixes to the following components: Automounter, Object Exchange over Bluetooth, Fax and modem, FireWire OHCI software, Password server slapd, SmartcardServices compatibility, setkey command line tool, Navigation Services, USB FHCI, and USB 2.0 hard drive mounting.
Sources tell AppleInsider that Mac OS X 10.3.9 is slated for a release in late March or early April.
I'll be extra slow to adopt 10.3.9 given the "big" (superstition) kernel version change, but it sounds promising. 10.3.9 will likely be the last OS update for my iBook, I doubt a G3 will be able to run Tiger well.