I've had my fully emerge -uDN world version 3.4e up and running for a few weeks with no wireless problems. I've been using NetworkManager, and loving it, and even have vpn setup to work using it. Since the middle of last week, after I boot, I see no wireless devices. I have to run the following:
# /etc/init.d/ipw3945d stop
# rmmod ipw3945
# modprobe ipw3945
to get my wireless back up and running. I fear that one of my updates screwed up the boot sequence. Anybody have any clues?