Apple Cinema Display Brightness no longer works in Mavericks or Yosemite
There are various threads on discussions.apple.com, but the solution I found on MacRumors I will not repost the solution there, since it's likely to be deleted since it's definitely a bit of a hack. 

But one that will extend the useful life of your Cinema Display for at least a few more months (if not a year or two): 


  I got the following .kext files from a computer running mountain lion.
  
  AppleBackligt.kext AppleBacklightExpert.kext AppleUSBDisplays.kext
  
  The files are placed in /System/Extensions
  
  Then i placed the kextfiles on the desktop, and ran a tool called
  "KextBeast". This app installs every kext file on the desktop. Then i
  rebooted and voilá..
  
  
  Get kext files
  Run KextBeast
  Reboot
  


"Running KextBeast" requires registering (i.e. potential spam) to download the KextBeast app.  

Here is how to do the same thing in the Terminal:

 # make certain you have the ability to run as root or admin (so you can "sudo")
 cd /System/Library/Extensions/

 # move the old kernel extensions out of the way
 sudo mv AppleBacklight.kext AppleBacklightOLD.kext
 sudo mv AppleBacklightExpert.kext AppleBacklightExpertOLD.kext 
 sudo mv AppleUSBDisplays.kext AppleUSBDisplaysOLD.kext

 # move the Mountain Lion kexts into position
 sudo mv ~/Desktop/AppleBacklight.kext .
 sudo mv ~/Desktop/AppleBacklightExpert.kext .
 sudo mv ~/Desktop/AppleUSBDisplays.kext .

 # set proper permissions and ownership
 sudo chown -R root:wheel AppleBacklight.kext
 sudo chmod -R 755 AppleBacklight.kext
 sudo chown -R root:wheel AppleBacklightExpert.kext
 sudo chmod -R 755 AppleBacklightExpert.kext
 sudo chown -R root:wheel AppleUSBDisplays.kext 
 sudo chmod -R 755 AppleUSBDisplays.kext

 # mv the OLD kernel extensions out of the way 
 # (or put them in the trash via the Finder)
 sudo mv *OLD* ~/Desktop


Reboot and voila!  You will have brightness controls with your "Vintage" Cinema Display.  

I hope this helps somebody else out.