Well I clicked on the 'update' icon when it popped its friendly face round the corner - as you do, seems rude not to. Anyway, after a reboot my Wifi was bust [pulls sad face]. So after a few minutes fidling with no success I viewed the restricted driver page only to find a second restricted driver claiming to be for the Atheros Wifi card - and subsequent to my wishes it was active and thus meddling with my 'linux-backports-modules-intrepid' version of the atheros drivers. What's a nerd supposed to do these days, so many drivers and so little time.
Anyway, the rub is that I uninstalled the backports-modules and left the new restricted driver, 'Support for 5xxx Series of Atheros 802.11 wireless LAN cards', active. Did a reboot and hey-presto Wifi was working again with what I assume is the latest and greatest wifi drivers for the Atheros cards and my lovely AcerOne.
So if you're having problems with your Wifi after an upgrade try getting rid of any old drivers and use the restricted ones supplied built in with the latest kernel build - they seem to have been fixed.