Its been bugging me for a while now that I would intermittently have problems with my laptops intel N-6205 wifi card stop sending any data, even though it was correctly associated with an AP.
Then a few weeks ago I just accidentally noticed that it only actually happened when the laptop was running on battery power.
Finally today I remembered to have google around and first found this which lead me to here and so hey its an issue with the power management, even in intels windows drivers!
Finally I found: http://ubuntuforums.org/showthread.php?t=2058500
with the magic command:
sudo iwconfig wlan0 power off
(yes the command on the page misses including the network device name which of course is needed) and hey presto! no more failing to connect while on battery.
Now just need to add this to my init scripts and live with the slightly extra power draw on my 9cell!! extended battery.