The most recent header/kernel updates also broke things for me, too. After rebooting, brightness is stuck at full power.

Glad to hear it isn't just me. Any news on this? Its killing me (headaches).

Fixed for me with the more recent updates, too. Thanks!

I just noticed that it broke for me, too, and I realized that I had the 3.2.0-43 #68 kernel installed (not good).   I went to the sputnik-kernel ppa today to see if a new kernel is sitting in there (and it is).   The version in the ppa is 3.2.0-44 #69+kamal16~DellXPS.

I ran the following, rebooted, and now my backlight is back again:

sudo apt-get update && sudo apt-get dist-upgrade

That pulled in the #69 Kamal kernel for me and I just confirmed that the backlight is happy again.  My system is the original, non-FHD version running 12.04. 

And thanks to whoever out there silently fixed it!

Thanks for posting this!

This doesn't solve the same problem that just occured with 13.04.

Looks like what may have happened was a security update kernel (non-sputnik) jumped in ahead of the latest sputnik-kernel update and that's what may have led to the confusion about the backlight.  If you see update manager asking you to update (and you have the sputnik ppa configured), double-check that the kernel has the "kamal / XPS13", etc. in the package name before pulling the trigger.  I know that's not the most efficient way to address it but it's something to be mindful of. 

Kamal's repo doesn't support 13.04, so the problem remains even with a new kernel today versioned 3.8.0.23

13.04 is supposed to have the backlight support baked into it from upstream, hence, no need for a PPA.    I'm not sure what the problem is exactly, but there are two camps involved with this so far.    One set of users with the FHD XPS 13 running 13.04 are reporting that their backlights are working great with 3.8.0.22 while others are complaining that it *was* working with 3.8.0.21 and it doesn't with .22 and higher.   For anyone running into this now with the .22 and .23 kernels did anyone, by chance, have this kernel installed before updating to the latest bits?:

http://people.canonical.com/~kamal/lp1169376/

..or had anyone that's suffering from this been running with the pre-release 13.04 versions where the backlight was working, quit working, worked again with the kernel from the link above and then quit working again with the production kernels? 

 This is also being logged here in launchpad:

https://bugs.launchpad.net/dell-sputnik/+bug/1169376

If anyone is running into this on 13.04, this is the place to start logging information and any history you've had with your backlights.   The goal is to get this 'right' in the 3.8 kernels so that we're not having to lean on separate PPA's going forward.