Same for me. Downloaded the update via Windows Store, installed and rebooted to a black screen.
Powered off and on, pressed F8 and then got the same message:
"Couldn't update to Windows 8.1
Sorry, we couldn't complete the update to Windows 8.1. We've restored your previous version of Windows to this PC.
0xC1900101 - 0x40017"
XPS 15 Laptop, i7, 8Gb RAM, Win 8Pro
Called Dell Pro Support and they believe it is an Nvidia driver issue, but due to the number of people having the same problem said it's probably best to wait for Microsoft to offer a fix as it has been logged with them.
The update has been a long time coming and been through preview so it should work, obviously I'm delusional and live in dreamland.