For anyone updating to 10.5.8, here's what I did:
First I tried updating (using the downloaded delta patch, not through Software Update), using rfca's patches (in the Tools folder on the SD card) for both the graphics kexts (AppleIntelIntegratedFramebuffer, AppleIntelGMA950) and IOBluetoothFamily. The patch didn't work on the graphics kexts and resulted in a system that was unbootable in either normal or safe mode. I then restored my 10.5.7 backup (which you should always make before a OS update, even on a real Mac) and tried again.
This time I updated, again with the delta patch, then rebooted normally. Like when you updated to 10.5.7 just after installing, it'll reboot itself on your first try to boot it, then boot normally. This time, I used the graphics drivers from the System/Library/Extensions folder on the SD card (i.e. the same ones I had been using on 10.5.7), and just used the patch on the Bluetooth kext. This worked fine. I've been using 10.5.8 for a while, and there seems to be no problems as long as you reinstall those three kexts. I installed the three kexts with Kext Helper, then repaired permissions and cleared the extension cache before rebooting.
Also, to use the Bluetooth patch, copy /System/Library/Extensions/IOBlueToothFamily.kext to some folder. Put the IOBluetoothFamily.kext.patch file somewhere, then open the terminal and cd to the folder where the kext is and do "cd IOBlueToothFamily.kext", then "patch < (full path to IOBluetoothFamily.kext.patch)". It'll ask you for the location of the file to patch (I couldn't figure out the right -p option to use to just do it automatically). Enter "Contents/PlugIns/BroadcomUSBBluetoothHCIController.kext/Contents/Info.plist", and it'll indicate success. Now you have a patched Bluetooth kext you can install with Kext Helper.
You could just reinstall the already-patched Bluetooth kext from the SD card, but there are a lot of Bluetooth fixes in this update, so I wanted to make sure I had the latest.
Also, one thing I've noticed is it seems to take longer to boot. Not a whole lot longer, but noticeably so. No big deal really.