UPDATE - 11-24-2015
If you need AFS access on Mac OS X 10.11 El Capitan, and do not mind some limitation (terminal only), we do have a working solution. You can download a client from Auristor via https://www.auristor.com/openafs/client-installer/
If you are using OS X 10.11 (El Capitan), download this client installer.
If you are using OS X 10.9 or 10.10, please download this version of OpenAFS client.
For OS X 10.7 - 10.8, please download the appropriate OpenAFS client relative to the version of your Mac OS X version from Stanford ITS. You can determine your version by going to the Apple logo on the top left-hand corner > About this Mac.
If you have a previous version of OpenAFS client installed, please uninstall it by using the Uninstall script located inside the dmg file (under Extras) you downloaded in step #1, then reboot the machine. *IMPORTANT*
Once the machine is rebooted. Proceed with the installation, and then open Applications > Utilities > Terminal, and do
sudo bash -c "echo cs.stanford.edu > /var/db/yfs/etc/ThisCell"
Reboot once more. *IMPORTANT*
Open System Preferences > OpenAFS, check the boxes that say "AFS Menu" and "Use aklog"
Click on the OpenAFS icon in your task menu on the top right-hand corner and click "Get New Token"
Enter your csid@CS.STANFORD.EDU and your password, upper case is required for CS.STANFORD.EDU.
If everything is correct, your task menu icon should change to and you should now have access to your AFS directories. I found it convenient to use Finder > Go > Go to Folder (or use keyboard shortcut command+shift+G) and type /afs/cs.stanford.edu/u/yourcsid
You can also create a symbolic link to your home directory by going to Terminal and do,
ln -s /afs/cs.stanford.edu/u/yourcsid ~/Desktop/yourcsid
The above instruction should apply to most modern version of Mac OS X (10.9, 10.10 ...etc) Please let us know via https://support.cs.stanford.edu/hc/en-us/requests/new if you have any problem.
For Advanced User
The above instruction would change your default kerberos realm to stanford.edu from CS.STANFORD.EDU or any other realm you may have set. For convenience, you may want your kerberos realm to default to CS.STANFORD.EDU and here is how.
Default kerberos realm
The simplest way is to backup the existing kerberos conf file at /Library/Preferences/edu.mit.Kerberos, and download a CS specific krb5.conf to /etc/krb5.conf.
Since /Library/Preferences/edu.mit.Kerberos take precedence to /etc/krb5.conf, it is important that /Library/Preferences/edu.mit.Kerberos is absent.