Ouch. I never really thought about the implications of renaming your home directory in the Mac world, but since Mac OS X is running atop Unix (FreeBSD, to be specific) this is a very bad thing.
The biggest problem is that when you next reboot your system, it'll complain that you no longer have a home directory (since it's probably looking for something like /Home/taylor but you've ingeniously renamed it /Home/dave) and might either refuse to let you log in or drop you in a generic directory like / or /tmp.
To fix this, you need to restore the name of the existing directory, not move files into a new directory, and then you'll have the magic set of preference and configuration files you seek, all in your Library/Preferences folder within your home directory.
(Actually, Mac applications aren't that well behaved as a group, so some actually use subdirectories in your Documents folder (like Microsoft apps, which use "Microsoft User Data" within "Documents") or elsewhere to store preferences and configuration options too.
If renaming your old home directory doesn't fix it, then dig around and see if you can identify where the preference files have gone, because they're what controls whether an app thinks you've used it and tweaked it or not.
In terms of why was it so easy to do, well, that's why I think it's a good idea to run on a day-to-day basis as a regular, not admin user. By being an administrative user, you get greater powers and as the proverb goes, absolute power corrupts. Only this time it was your hard disk that was corrupted...
In the future, when you want to rename your account or, more sensibly, create a new account, your best bet is really to use the Accounts tool, accessible from Apple --> System Preferences --> Accounts:
Notice the "+" on the lower left there? Click on that and you can add new accounts to your heart's content. Also notice that Linda's account on this system is listed as "standard", that is, not an administrative account. It's safer.
Good luck to you!
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For info on how to change the short user name (which is the greyed out box in the screen cap and the name used for the home folder) check out the excruciating process described by Apple:
http://docs.info.apple.com/article.html?artnum=106824
...or this donationware app:
http://www.versiontracker.com/dyn/moreinfo/macosx/23494