Just downloaded and installed Ubuntu Natty Narwhal (11.04) on Lenovo B460 and the wifi didn't work at all. I had done an upgrade from 10.04, I thought it was some screw up during upgrade, but even a clean install didn't help. The network icon showed an annoying "Wireless switched off by the hardware switch" message even though it was turned ON. After googling it for a while, I found the solution:
acer_wmi module which is inserted by default is the offending module.
Check if acer_wmi module is running by doing
$ insmod | grep acer
Knock it off by doing:
$ sudo rmmod acer_wmi
Also to disable the module getting loaded during subsequent boot up, blacklist the module by adding the following line in the file /etc/modprobe.d/blacklist-ath_pci.conf:
Reboot the machine and launch the "Additional drivers" application and activate the Broadcom wi-fi driver and you're done!