No sound after upgrading to Lion, despite hardware working fine After upgrading to Lion, I have no sound at all under OS X.  It doesn't come through my speakers or through my headphone jack.  I've checked in the Sound preferences, and it's set properly.  I've tried killing coreaudiod, which does nothing.  I've triple-checked that I'm not muted (I'm not) and the volume is up (it is), and I've made sure I'm upgraded to 10.7.1, since that was supposed to resolve some sound issues.  There's just nothing.

The good news is that I know that the hardware's not broken, since my Widows BootCamp partition works just fine.  The bad news is that I don't want to boot into Windows to listen to iTunes.

What am I missing?
Odd though it may seem, try launching Garage Band (if you have it) and creating/saving a new project. It seems that Garage Band does some low-level tests on your audio system when it runs, and clears up weird states like you're encountering.

This doesn't answer the question of what's wrong, but hopefully will fix it anyhow.