I tried those on Windows 7 and after rebooting couldn't log in anymore - it just kept saying my username or password was incorrect.

It took me quite a while to figure out that this was because I had set my keyboard for the logon screen to Cyrillic. I confirmed by overwriting sethc.exe with cmd.exe and enabling high contract - the text I typed in the command prompt window that opened was in Cyrillic. (Not my own trick, but a very useful one for recovering access to Windows without directly editing the registry files!)

That's quite a downside, I would say! Turns out all those Microsoft warnings that say "do not modify the registry unless you know what you are doing" had a point.