Update was a no go for me.. System details on the left. Basically, it works great except that I have no display out! I can SSH in, Plex and iTunes (using a remote app on my phone) are working fine, and I even see that Time Machine backups were completing.
The only way I could get the display to work was with nv_disable=1. I booted and updated the NVidia alternate drivers (which I don't need for my card, but use), and had the same issue occurring. So I again booted with nv_disable and uninstalled the Nvidia drivers through the control panel uninstaller. Rebooted and....same issue.
Currently in the middle of an estimated 5 hour Time Machine rollback.
When I tried to boot my recovery partition with nv_disable, I got a gray screen. When I also set to GraphicsEnabler=No, then I got a gray screen with the spinning beach ball and nothing else. However, when I used Clover from the original USB installer created using Tony's El Capitan install guide, recovery booted fine. It sounds like I have some flags messed up in my Clover config, but it was working fine on 10.11.0!
I'm rolling back now so that I can use my system, but I'll tackle the update again over the weekend if anyone has any ideas on what I might need to tweak? Maybe just uninstalling the Nvidia drivers before upgrading will do it. I'll report back!
EDIT: I'll point out that I disabled the onboard graphics in my motherboard setup, if that could have anything to do with this..