How do I do a clean install of Yosemite?
I downloaded the OS X Yosemite GM from the App Store.  Quit the installer that pops up with out installing and made a bootable flash drive with it on it.  Used the following command below just change the paths to fit your need.

sudo /Applications/Path to *Yosemite Installer*.app/Contents/Resources/createinstallmedia --volume /Volumes/*FlashDrive* --applicationpath /Applications/Path to *Yosemite Installer*.app --nointeraction


Then booted the computer to the usb flash drive and wiped the previous partitions using Disk Utility.app and installed a fresh copy.