Comment 6 for bug 94566

After recent update of Ubuntu the problem seems to be solved.
2.6.22-9-generic (package version 2.6.22-9.25)
alsa-base 1.0.14 (package version 1.0.14.1ubuntu1)

File ' /etc/modprobe.d/alsa-base' contains the following line:

options snd-hda-intel model=lenovo

How it's working now:
 * Muting 'front' channel mutes the speakers
 * Changing 'front' level (volume) with volume weel un-mutes the speakers
 * Plugging headphones into the front jack mutes the speakers
 * Unplugging the headphones un-mutes the speakers
 * Checking 'headphones' mixer option actually gives sound to the front jack

Mic, front mic, mic boosts also work as intended.