I should report that I do not experience the bug you mention (on a Thinkpad T60, with the intel device in question) after upgrading from 10.04 to 10.10 (maverick).
I tried several different WiFi-settings, different encryptions and never experienced any slowdown at all.
My kernel is 2.6.35-24-generic and my wpa_supplicant is 0.6.10-2.
NetworkManager is used, and has version 0.8.1+git.20100810t184654.ab580f4-0ubuntu2
I should report that I do not experience the bug you mention (on a Thinkpad T60, with the intel device in question) after upgrading from 10.04 to 10.10 (maverick).
I tried several different WiFi-settings, different encryptions and never experienced any slowdown at all.
My kernel is 2.6.35-24-generic and my wpa_supplicant is 0.6.10-2. 20100810t184654 .ab580f4- 0ubuntu2
NetworkManager is used, and has version 0.8.1+git.
I hope this helps.