I’ve been searching for this all afternoon! The old way of resetting the OS X setup assistant via single-user mode and directory services dscl no longer works in Yosemite (and possibly Mountain Lion and Mavericks; I haven’t tried it since Lion). I discovered a new way by running across this engadget post. I modified step 5 to include the users folder. Here’s a quick summary:
Boot into single-user mode by holding down Command-S on the keyboard during startup
At the command-line prompt, type mount -uw /
rm -R /Library/Preferences
rm -R /Users/YOURUSERNAME/ <– replace YOURUSERNAME with whatever your user name is
ls (to list the files)
Delete the file that is named after your user account with a .plist extension. For example, for user name “stevesande” you’d type rm stevesande.plist
For my purposes, I omitted step 3 and everthing worked fine.
Some people have ran into a problem with creating a bootable USB installer for the Yosemite Beta. The script located in the Installer app called “createinstallmedia” does not work quite yet on Yosemite like it did in Mavericks. I kept getting an error that told me my volume wasn’t a valid mount point.
After doing some research, I came across a post on MacRumors.com that had a workaround. Just run the following commands in Terminal and you’ll be good to go!