How can I limit users to one account each? (Or, how can I detect users who have multiple accounts?) For various reasons I would like to limit each individual user to registering/using only one account.  I realize that there is no perfect way to do this, but what can I do within Drupal to detect cases where users have registered and are using multiple accounts?

I plan to set up a view using uiplog to check whether the same IP address is logging out and then immediately logging in to another account, but what else can I do?

Additional information: The site I am working on requires users to complete a fairly lengthy registration form and then additional information on the first time they log in.  As such, I'm primarily concerned about users with multiple accounts trying to game the ratings system within the site.  (Abusive users will be handled through an abuse reporting system.)
You can not. Only limitation is Useraccount with one Emailadress. But if the same User Logs in with a different name and a disposable email adress, you can not verify if it is the same User. Something like undisposable will help. But it's not the solution.

Also if 200 Users use the same Proxy/same IP, you will limit them.