Comment 13 for bug 730972

1.Install the Non-free Broadcom STA Driver via 'Additional Software'
2.To check if my suggested solution will work for you, try to run the following command in terminal
# sudo modprobe -r acer-wmi
after that you should be able to connect to wireless lan (should work for acer travelmate & lenovo ideapad with broadcom wireless adapters )

3.If that worked out for you, the following procedure will resolve the issue permanently with not working wireless/wlan broadcom adapters:
# sudo gedit /etc/modprobe.d/blacklist.conf

in the blacklist.conf file add at the end this:

blacklist acer-wmi

4.You're done.