I'm stuck in 'root' user mode

Essentially, you enabled the root user correctly (the steps are @ http://support.apple.com/kb/ht1528)

The only thing you "Added" when you enabled the root user was the ability to login and use the root user account.

What is happening is that you are logged into the root user right now, and need to log back into your admin user account. Do this by clicking on the top-left corner menu Apple > Logout..

Once you get to the login screen, you will need to then login with your existing admin account username and password. The only thing that you changed when you enabled root was added the "other..." part of the login window/screen, your other user account is still on your computer.

Once you've logged into your admin account, follow the steps from the article to disable root (I added it below for Lion/Mountain Lion)

How to disable the root user

OS X Lion

1. From the Apple menu choose System Preferences....
2. From the View menu choose Users & Groups.
3. Click on the lock and authenticate with an administrator account.
4. Click Login Options....
5. Click the "Edit..." or "Join..." button at the bottom right
6. Click the "Open Directory Utility..." button.
7. Click the lock in the Directory Utility window.
8. Enter an administrator account name and password, then click OK.
9. Choose Disable Root User from the Edit menu.

After choosing to disable the root user, you can just exit out of the windows that are open.

The pad lock icon at the bottom left of system preferences/directory utility windows doesn't really matter except that it either allows or prohibits you from making changes on the options.

And if logging into your user account doesn't work at the login screen, what exact error/behavior are you encountering? Do you have the user: and password: fields that you have to manually type in your information? or is your login screen setup to just click on a user account name, and just enter the password?

It's highly unlikely your user account changed so long as you didn't make any changes/modifications to anything while in the root user.

If you still are unsure if/what the user account name is or if it's still there, you'll have to log back into root & go to system preferences > users & groups to see if your user is listed. Use this username to login with at the login screen.

** ONLY FOLLOW THE STEPS BELOW IF YOUR ACCOUNT ISN'T LISTED IN THE USERS & GROUPS **

If it isn't, open up a finder window while logged into root and click on the menu @ the top " Go > Computer ", then select "Macintosh HD" - then the folder "Users" (so you're in "Macintosh HD/Users/" folder)

you should see a user folder that contains your data there, so again, IF your user account doesn't exist in system preferences > users & groups, you'll need to create a new user account, and most importantly the following:

ACCOUNT TYPE: administrator

LONG NAME: The name you want your account to say. Ex: "Remy G"

ACCOUNT NAME: THE NAME OF THE FOLDER IN THE /USERS/ FOLDER THAT HAS YOUR DATA (Ex: "remy") -- This name MUST be all lower case, and no spaces to be a valid account name

PASSWORD & CONFIRM PASSWORD

After entering all data, hit "create user" and it will say something like "a folder already exists with the same account name, would you like to use this existing folder for this account?" You would then click use existing folder, then try logging in with it again.