<< or you can stuff their pre-paid envelope full with store ads and send it back to them >>
I just thought you might like to know that you are commiting a crime with a severe fine if you get one of those companies angry enough to press charges.
<< Ive had tons of friends who get those in the mail and such, apply, and are rejected. Why do they even send those things out? >>
Many companies look at your credit rating. If it is high enough, they "pre-approve" you and send you an application. However, the credit rating is always (1) old data and is (2) never enough data.
Here is an example of (1): If you recently lost your job, then your credit rating will drop (length of employment is one part). By the time the application is mailed back to the CC company, your credit rating may reflect the new worse score (thus disqualifing you for the CC).
Here is an an example of (2): The credit rating doesn't include your income. Often you might have a great credit rating but not enough income for a particular card. The CC company has no way of knowing if you have a high enough income when they send you a "pre-approved" application. When you send it in with your income stated, you might find that they reject you due to your low income.
All CC applications that are "pre-approved" have a disclaimer in small print that mentions all of this. If you make less than $15,000 a year don't apply to a Platinum CC (unless it is a platinum student CC) since you will almost always be rejected.