A problem with Debian and Ubuntu (and possibly other distros) is that the ipw3945 module fails after a large amount of activity.
The solution is very simple, but it took a lot of work to find it.
Edit /etc/modules and put the following in there
iwl3945
Edit /etc/modprobe.d/blacklist and add
blacklist ipw3945
That’ll do it. The iwl3945 module performs just as well on sftp transfers, and I havn’t noticed any problems with it.