I just installed Xubuntu 13.04 on a new Dell XPS 13 Ultrabook. When I boot up the screen brightness is EXTREMELY dim. Adjusting the screen brightness doesn't do anything. This is obviously a very new bug with 13.04.
here are a couple kernel boot parameters you can try
Along with @GM-Script-Writer-62850's answer, if you're using an EFI BIOS boot, you ned to go into the BIOS setup and set "Load Legacy Rom" to Enabled.
I have experimented with the minimal GRUB line to get this working and I only need
AFAIK Legacy is anything not Windows 8, and I've not experienced any performance hit.