Mine completed the update, seemingly in correct fashion, then went black the first time the screen saver kicked-in. Rebooting left it at the black screen. I could see the mouse pointer and the "waiting" circle when I moved the mouse, but it would disappear when stationary.
I found a posting from June and the preview release stating that it was a display driver incompatibility with the Intel HD 4000 graphics driver - reboot in safe mode and update the driver with the manufacturer's drivers.
That's what I did, downloading the most recently approved drivers for the Intel HD 4000 and nVidia graphics cards from Dell.
All is working now.
You'd think this would have been caught before RTM - maybe next time, they'll re-think the "no early distribution" decision prior to release.
This is not a solution that the average end user/home user would be able to figure out - a big issue for Microsoft.
On a more positive note, the Surface RT that I picked up at the global partner conference in Houston this summer updated on its own, no issues.