You can still use Disk Utility to repair permissions. It is located in Applications/Utilities. Perhaps the easiest way to get there is by clicking Finder's Go menu and then selecting Utilities. Double-click DU to launch it. In the DU window, select your hard drive and then click Repair Permissions (don't bother with Verify).
If you need to run Repair Disk, you have to boot from the Recovery partition that was created in Lion. Start up while pressing Command-R; release the keys when you see the Apple logo. You can read the complete instructions in
Preparing your Lion repair kit.
Let's see if I can give you a better idea of the usefulness of accounts. OS X was designed for multiple users, so that you don't need multiple computers for each person who needs a computer. Each user can have a separate account with its own email, preferences, desktop, etc., just as if he/she had a separate computer.
It is useful to set up an account for troubleshooting purposes. If you are having difficulties, diagnosing the cause can be helped by this. Lets say, for example, that Safari is crashing. The problem might be caused by something in your main account or it might be due to a problem outside of the User folder. To test this, you can log into the test account and try Safari from there. If the problem is gone, the cause is in your main account and you can troubleshoot from there. If the problem still occurs in the test account, the cause lies outside the Users folder.
In the Users & Groups section of System Preferences, click the lock icon to open it and enter your administrator password at the prompt. Then, click Add (+) and follow the prompts. I find it useful to make the test account an administrator account and I have named mine Emergency. Follow the rest of the prompts to complete the process.
When you want to log into the test account, go to the Apple menu and click Log Out. All apps will quit, the desktop will disappear, and you'll see a list of available accounts. Click the test account and you'll be in.
The test account will be pristine, as if nobody had set up any preferences, Safari bookmarks, email accounts, etc. It's probably best to leave it as unsullied as possible for testing purposes. When you want to get back to your main account, log out as before and then log into your main account. It will have been untouched.
