As far as I can see, no-one else is having this issue so wonder if this might be an interesting challenge...
I ran the Windows 8 upgrade assistant to upgrade from Windows 7 - installation seems to have run smoothly but the assistant seems to have skipped the user accounts pages and I now have view of a login screen with the right username, but no password works (I previously had no password at all!). I've also run a third party bootloaded application to confirm there is no password so at something of a loss.
Any idea how I can get logged in? I have no access to Windows whatsoever, the password is not being accepted, and I'm not being given the option to use my Microsoft / Windows Live account to login.