Comment 17 for bug 187980

It appears that difference between Feisty and Hardy is the appearance of the sony-laptop module in Hardy - this is overriding the sonypi module that handles the hotkeys. I suggest as an interim workaround to black list the sony-laptop module:

sudo vim /etc/modprobe.d/blacklist

and add the following line:

blacklist sony-laptop

reboot and let me know if this interim workaround helps.

I will investigate why the sony-laptop module isn't working correctly