I haven't done a ton of research on this yet, but I was wondering if anyone is experiencing loss of Internet connectivity with any distro ( I am using Linux Mint at the moment) running the IWLAGN driver with an Intel® Centrino® Ultimate-N 6300 mPCI-e card in any Thinkpad (I am running a T410). This only occurs running on 'N' mode and not on 'G" mode. It happens several times a day. If I use NetworkManager I can simply disconnect/reconnect and it starts working again. I haven't fooled around with pinging devices to see what is actually up or down at that point, but I will try that as well.
I have this problem with my Intel 4965-AGN on Ubuntu Lucid (v10.04).
If you search ubuntuforums you will find several items that discuss this with various degrees of resolution.
If you search launchpad, you will find bug reports (#604175 etc) about this item. It has been around a while.
Personally, I connected a wire network, completely removed network-manager and installed wicd instead.
I have had few wireless lock-ups or drops since. Hmmm. (If you don't connect a wire network, you cannot
do the complete removal then install of something else.)
Keep us posted on your progress,