There is an annoying bug on Toshiba Satellite Machines running Ubuntu Linux (seems variants up to Maverick) which means that plugging in to the headphone jack does not work and, also, that speakers continue to play sound.
The solution, after much digging, is to add:
options snd-hda-intel model=ideapad
to /etc/modprobe.d/alsa-base.conf
I've put in a bug report, so hopefully this can get a fix in Natty.