Comment 82 for bug 144621

according to http://benlynn.blogspot.com/2008/03/thinkpad-x61-wireless-and-ubuntu.html it's all about upgrading the iwlwifi microcode (which is what you should be doing if you're reading this looking for a quick fix).

I'm currently testing this fix on a Compal FL90+, also driven by the iwl4965 module.
I recommend pushing the fix out asap, the ucode has been available since November and this is hitting a lot (a lot!) of laptop users.