Raymond beats me to the punch (mine was going to be rant-i-er, but five times* as funny), on how the HKEY_USERS\.Default, despite having the word "Default" in the key name, isn't "The Default User" from which all others are initially spawned.
It's possibly the most frequent misconception I've hit in the user profiles space (which I don't really work in any more, but did quite a bit for a while there).
I even argue with colleagues about it from time to time; the most reliable way to win the argument is by loading up the NTUSER.DAT in the Default User Profile (that's the one on disk - C:\Documents and Settings\Default User) and modifying a value there, then creating a new user and noting the new value is part of the new profile. "Ohhh," they say. "You're so awesome," they say. "You look amazing too. Have you been working out?"
Where was I? Ah, right - Raymond calls the on-disk guy the template user; seems like a good name.
My pet name for .Default is "Mr Nobody". If I thought I could swing it, I'd get the key renamed to .Nobody, but there's buckleys of that happening.
Windows 95 might have used Mr Nobody differently (back then, called the CancelMan, cos you could log in to the default "profile" just by hitting Cancel at the password dialog, unless... steps... had been taken - anyone else have loads of fun with POLEDIT and the CancelMan in '95?) in a profiletacular way, but profiles weren't on by default anyway, so I might just be misremembering and blathering.