Another one of those 'just-in-case-it-helps-someone-else' posts:
Overnight I upgraded to the newest version of Ubuntu, and this morning I found that I have no sound. I toyed around with many of the proposed fixes (many of which I realize are out-of-date) before realizing that for some reason my system defaulted to the 2.6.25-386 kernel instead of the 2.6.27-generic. I manually edited grub's menu.lst to default to the newer kernel and rebooted. My sound came back right away! I then did something I always mean to do but never do: I went back and uninstalled all of the old kernels left over from previous updates. I got rid of ~500MB of space and am using the latest stable kernel. Yay!
