I did this a little while ago and it worked like a charm. On the FTC's website they have a phone number where you can call and temporarily opt-out. The recording then references the site below. At the site you can permanently remove yourself from Experian, Equifax and TransUnion's lists of people whose credit scores they can give to lending companies, thus giving them the ability to send you preapproval offers in the mail.
I felt obligated to do this after receiving a card in the mail for a CL of $6,000.00 where all I had to do was call and activate it. To think what could've happened if an identity theif happened upon that card!
Here's the site:
*This site is government-sponsored, so your information is protected
Here you can temporarily remove yourself from the list for 5 years by filling out a simple online form. You can also print out a form, complete it and send it in to permanently remove yourself from the list. 
This is a great tip. I opted out about 6 months ago, at the advice of a friend in law enforcement, who told me about a few ID theft cases involving stealing "pre-approval" offers.
Another thing I did a few years back, was call ALL of my credit card companies I have accounts with, and told them to stop sending me any blank "balance transfer" checks. I told them that if *I* need checks, I'll request them. Back in 1998, someone stole blank checks that MBNA sent me in the mail, and did some serious damage. It took me 3 months to clear my good name.
Credit card companies send them out like candy, not realizing of the harm that can happen if they fall into the wrong hands. Nowadays, it's so easy to balance transfer electronically anyway.
Credit card companies send them out like candy, not realizing of the harm that can happen if they fall into the wrong hands. Nowadays, it's so easy to balance transfer electronically anyway.Message Edited by Ishmael109 on 09-03-2008 10:58 AM