This is the answer to the million dollar question: disable the AC adapter / power cord beep in Acer Aspire One AO722 netbook in Ubuntu 11.10.
It is easy in Windows and perhaps earlier versions of Ubuntu.
In U11.10, you need the command line. First bring up the terminal, e.g., use ctrl-alt-t.
Then use the utility
For portables there are no separate system speakers for the system beep, therefore the desktop methods won't work. For some portables, there are two devices, one for the digital HDMI and one for the analog speaker and headphones. You have to pick the correct one for the volume settings.
For the AO722, use F6 to pick the conexant sound card, rather than the first HDMI sound card.
Then use the arrow keys to get to the beep column. Type m to toggle the muting status.
The heart attack beep will be off when the power cord is attached or removed. But the beep is not altogether muted. The beep volume seemed to be coupled to the master volume or the alert volume.