I'm having the same problem, on a Thinkpad T410.

Sound worked fine until December 2012. Not sure what prompted the failure. Since then I've updated to Ubuntu 12.10 and it remains a problem.

In Ubuntu: no sound from the speakers, but the headphones work fine.

What is strange is that I am ALSO having sound problem when I dual-boot into Windows. There the speaker audio works *intermittently*. The sound will come on for a few seconds after I change the volume using the +/- buttons above the keyboard, but then it stops working again.