Comment 2 for bug 714163

I'm also experiencing this issue using xubuntu - since it is a derivative of ubuntu it makes sense that it appears there also.

It appears this is related to overzealous power management for the wireless card when on battery; on my system the wireless card is eth1 and it's power management setting on battery is 'All packets received'. Switching it off by issuing a ' iwconfig eth1 power off' will fix the issue, and doing something like

#!/bin/sh
/sbin/iwconfig eth1 power off

and saving it as /etc/pm/power.d/wireless will fix it across reboots. There may be better ways to accomplish this whilst still retaining some power management, but this will restore functionality.

I agree that there should be some level of power management to help preserve battery life, but the current behavior of power management for wireless cards has a crippling effect on battery power. I consider it a rather critical bug, and suggest that it be addressed as such and a fix pushed out as an update quickly.