I'm no registry expert, but I wouldn't be led to your decision by the name of this file, ntuser.dat.
From my reading of it, it doesn't contain information that would compromise a users privacy. It simply contains personal settings, and screwing with it would most probably corrupt it, and cause you major headaches.
Again from Wilders link:
QUOTE
The user profile includes environment variables, personal program groups, desktop settings, network connections, printers, and application preferences.
I really wouldn't worry about this file as it simply contains a users settings, and not stuff like other .dat files hold. You really could break something if you mess with it.
You can add it to be included by CCleaner, and CCleaner ignores it. There's a reason for that I would think, but I'm not one of the development team.
EDIT: I think it worth mentioning that I have a lot of stuff on my PC with no doubt a shed load of settings built up over the last 3 years, and my ntuser.dat file is only 14.5mb. That's nothing on the scale of todays hard drives.