Comment 82 for bug 630748

Discovered which workaround works:
in /etc/modprobe.d/iwlagn.conf
options iwlagn 11n_disable50=1 11n_disable=1

Prior to using that workaround my wireless would crash almost immediately when I attempted to do anything more than very low speed web browsing, requiring a modprobe -r/modprobe of iwlangn. This is on natty 11.04 with module-init-tools 3.12-1ubuntu6