I downloaded the latest drivers from Intel and did a clean install (actually it only worked after 3 installs!) I also changed the channel on the router to 11. Now it seems to be working. I suspect the problem is caused by the driver in W8, but never the less the drivers offered by Dell did not work 
I recently purchased a XPS 12 with windows 8 x64 preinstalled. I have not been able to maintain a stable connection to my WLAN. However 7 other devices (laptops etc.) are all connected without problems. Only the troubled computer is running W8. I have the most recent drivers for the Centrino as well as the ProSet and chipset (and everything else) download on 14th March from Dell. Occasionally it connects, but after a few minutes it disconnects again. Sometimes I get Media disconnected and other times a limited connection where the data from the DHCP server could not be collected. Seems very irrational! The configuration is default from Dell. Any ideas?
Intel Centrino Advanced-N 6235 issues with Dell XPS 12 (Windows 8 Pro, 
"Disconnects / Media Disconnected")