I'm getting a non-boot after installing the update as well. I've generally had great experiences updating "natively" using Clover on Yosemite but this one failed for me. Same as rgardner, cannot safe boot, can't boot to recovery, and can't boot using external thumb drive. Nothing interesting logged in verbose output. I reinstalled Beta 1 on top of my existing installation and that got it up and running again (without b2 updated obviously) but at least I didn't lose my setup completely. I will wait for some other people smarter than me to check it out.This update may botch your install. If you need your machine for something critical I would wait on this one before jumping in