Comment 38 for bug 735171

761176 has more people still affected by this. I followed the idea in that bug to try the ppa kernel - Looks like the fix is in there.. I'm back to >5 MB/sec on 802.11n links with it.

$ uname -a

apt history for the upgrade
Start-Date: 2011-05-27 20:01:03
Commandline: apt-get dist-upgrade
Install: linux-image-2.6.39-0-generic:amd64 (2.6.39-0.5~20110427), linux-headers-2.6.39-0:amd64 (2.6.39-0.5~20110427, automatic), linux-headers-2.6.39-0-generic:amd64 (2.6.39-0.5~20110427, automatic)
Upgrade: linux-generic:amd64 (2.6.38.8.22, 2.6.39.0.1~20110419), linux-headers-generic:amd64 (2.6.38.8.22, 2.6.39.0.1~20110419), linux-image-generic:amd64 (2.6.38.8.22, 2.6.39.0.1~20110419)
End-Date: 2011-05-27 20:03:30

apt-cache policy linux-image
linux-image:
  Installed: (none)
  Candidate: 2.6.39.0.1~20110419
  Version table:
     2.6.39.0.1~20110419 0
        500 http://ppa.launchpad.net/kernel-ppa/ppa/ubuntu/ natty/main amd64 Packages
     2.6.38.8.22 0
        500 http://archive.ubuntu.com/ubuntu/ natty/main amd64 Packages