Comment 8 for bug 1103314

This became an issue for me too as soon as I upgraded to Raring. I have the "Intel Centrino Advanced-N 6205 Wireless" chip. Because I wasn't sure if this is the same chipset and bug, I filed a new bug, possibly a dupe, here: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1177591. I also confirm that disabling n and rebooting restores normal speed.