For me it goes most of the way through the install to the "just doing a few more things" stage then the screen goes black and the circular loading animation just freezes. Sits like this until I reset then the system rolls itself back to 8 and puts up an error message saying Windows 8.1 could not be installed. Tried twice...can't get it to take the update.
Puts up a seemingly generic error code 0xC1900101 0x40019
Not sure exactly where the best log files would be to figure out what it's doing/not doing. Everything I've looked at so far seems fairly normal.