Fix disabled wireless in Ubuntu on Lenovo laptops

2014 edit: If you’re experiencing problems on Ubuntu 14.04 with wifi on your Lenovo laptop with a Centrino wifi chipset, try disabling wireless N.
See http://ubuntuforums.org/showthread.php?t=2208210&p=12943350#post12943350

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Just updated my laptop to Natty Narwhal and I may write something about it in the future (spoiler: Unity sucks). Anyway this post is just about the solution I found for the broken wireless network manager applet in Ubuntu 10.10 and 11.04 in Lenovo B450 and probably most other Lenovo laptops.

Ever since I upgraded my laptop to Maverick Meerkat, my wireless isn’t automatically enabled on startup. It was no big deal back then since I could just simply tick the Enable Wireless in the network manager applet. But when I upgraded to Natty Narwhal, my wireless was permanently disabled.

After hours of trial and error, I found out the culprit. Running sudo rfkill list showed that I have an “acer-wireless” even though I wasn’t using an Acer machine:

bry@Abraxas:~$ sudo rfkill list
0: acer-wireless: Wireless LAN
        Soft blocked: yes
        Hard blocked: no
...

The solution to this was simple: disable it by adding blacklist acer-wmi at the end of /etc/modprobe.d/blacklist.conf.