Since the problem with (un)plugging the AC power doesnt happen under windows (i think i remember someone saying he also didnt have this under fedore/arch, but not sure) it actually is a software/kernel issue.
At the moment I am running the latest bios with kernel 3.6.0 from the official ppa. This is the moste stable combination I found after some tests, but it still suddenly shuts down when the battery is low (<30%) and heavy duty on the cpu...
I am an Ubuntu user since almost 8 years and this issue with zenbook is taking me to evaluate the return to Windows. This pc is indispensable for my job and in this condiction is unusable.
I am very sad, and this for me is an hard defeat..