I am currently running Ubuntu 13.04 on my I7 Hp Spectre Xt ultra book (which is a sweet rig FYI).
I was running Ubuntu 12 before with zero issues but when upgrading to Ubuntu 13 the wireless suddenly stopped working.
There are quite a few people with similar issues relating to the additional 3rd party drivers which get blocked when you upgrade (Check here first if you are having issues).
This however was not my issue, After stumbling around the internet for a few days I found someone who reset the Bios which resolved the issue, I over looked this earlier as I had not adjusted the Bios in any way so it would seem odd that this causes a wireless issue after an OS update.
However, this was the cause of my problem! I reset the Bios back to factory defaults (which I am sure they were anyway having not played with them on this laptop) and rebooted.
Suddenly the wireless started working straight away which solved my issue (have been running it for a few weeks since with no issues).
So if you are having issues with Ubuntu 13.04 after upgrading from Ubuntu 12 (or not upgrading even) I suggest you try resetting the Bios as a fix for this issue.