Update: January 16, 2015. This problem persists, even by judiciously following the instructions below. The newest solution I have is to install Linux Mint. Which I did. And the wireless is now working for the first time since I purchased the laptop a few years ago. The great sputnik project is officially dead. Long live Linux Mint!
Update: January 15, 2015 This problem is now best fixed by following the instructions here and turning off the disable 11n hack.
Update: June 23, 2013 I upgraded Ubuntu from 12.04 LTS to 12.10 and the wireless problems are solved. If you perform this upgrade there is no need to do the work-around below. I received a Dell XPS 13 Developer’s edition ultra book just the other day. It had Ubuntu 12.04 LTS pre-installed. It has a Centrino Advanced-N 6235 wireless card from Intel. The first thing I noticed was that the wireless network was flakey. I could connect and use the network for a short time, then it would freeze up. The syslog said simply:
ieee80211 phy0: Hardware restart was requested
After much searching I found a solution. First check to see if this fixes your problem (on the fly):
sudo modprobe iwlwifi 11n_disable=1
If it fixes the problem make it permanent by editing (or adding) a file called /etc/modprobe.d/wlan.conf and put the following line in it:
iwlwifi options 11n_disable=1