I don't know about anyone else, but upon installing 10.2 (Jaguar), I found all my system's audio, from alert sounds to MP3's to be weak, unfocused and lacking all bass. Pre 10.1.3 versions sounded the same as well, but after the 10.1.3 update, all audio was perfect from my iBook.
I wondered if it would be possible to revert the sound drivers back to 10.1.x, and searched around the /System -> Library -> Extensions folder and found a file named AppleOnboardAudio.kext.
I figured if I replaced the kernel extension with the previous version, things should be back to normal. I used Pacifist to extract the AppleOnboardAudio.kext from the 10.1.3 update package and used the Terminal to replace the newer version (I'd keep a backup, just incase). After a reboot all audio was exactly as it had been before Jaguar.
I've heard quite a few complaints from others about sound quality in Jag-wire, so if you're one of them, here's your fix.
[Editor's note: Clearly this hint falls in the Highly Experimental category! I have no idea of the possible downsides of running an older audio extension with the current system ... so if you try this, please proceed with caution - backup early and backup often!]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020828094307732