Comment 382 for bug 621265

On my Ubunt 11.04 machine, I installed
linux-backports-modules-cw-3.0.0-natty-generic

which gave me the new wireless modules without having to update to the latest Linux 3.0 kernel.

I also had to setup the "disable_hw_scan=0" as described in #370.
creaate this file,

/etc/modprobe.d/iwl3945.conf

and put this into it.
options iwl3945 disable_hw_scan=0

So far no more speed slowdowns.

Here are my system details,
lspci -vnn |grep -A3 Wireless
0c:00.0 Network controller [0280]: Intel Corporation PRO/Wireless 3945ABG [Golan] Network Connection [8086:4222] (rev 02)
 Subsystem: Intel Corporation Device [8086:1020]
 Flags: bus master, fast devsel, latency 0, IRQ 47
 Memory at f6cff000 (32-bit, non-prefetchable) [size=4K]

uname -a
Linux d630 2.6.38-12-generic #51-Ubuntu SMP Wed Sep 28 14:25:20 UTC 2011 i686 i686 i386 GNU/Linux

lsb_release -rd
Description: Ubuntu 11.04
Release: 11.04
Thanks for everyone who posted their information to help figure out this issue.