Comment 3 for bug 1341068

The description here isn't very informative. It's slow compared to what? The same machine booted in Windows? Previous Ubuntu releases?

One probable cause is that transmit aggregation as been enabled by default for some Intel hardware due to firmware bugs which caused unstable connections, which will definitely impact performance on 802.11n networks. If you know that your hardware worked fine with a previous Ubuntu release, or if you just want to see if it helps, you can boot Ubuntu with the iwlwifi.11n_disable=8 option to force transmit aggregation to be enabled. If you find this helps and gives you a stable connection, you can make this option permanent by creating a file named /etc/modprobe.d/iwlwifi-11n.conf which has the following text:

options iwlwifi 11n_disable=8