I have a Dell D620 laptop - whose sound died immediately after installing Ubuntu 9.10 Karmic Koala.
After much difficulty here was the fix: sudo apt-get install gnome-alsamixer
Then go Applications > Sound & Video > GNOME ALSA Mixer , and turn the sound back on - WHEW!
So if you have intel HDA onboard audio (snd_hda_intel) that died on upgrade - try it out!