I like using one email account for all of my email needs and one way I try to cut down on possible spam or unwanted emails is to use subaddressing when I sign up for a new service. It's certainly not foolproof but it does provide an easy way to filter mails when that "Unsubscribe Me" link suspiciously fails to work.
Subaddressing is simple to use, that's the main reason I like it. Gmail supports this, as it should since it's included in the email RFC. To use subaddressing, simply add a plus sign after the "local" part of your email (the section before the @domain.com). So, if you were signing up for Great Minds, you could use this email: firstname.lastname@example.org.
The problem comes in when people try to validate your email before allowing you to sign up. Many, many web services will not allow plus signs when you sign up, with varying degrees of success when it comes to handling a user who inputs the plus sign. Most services just reject the address as invalid and force you to try again. Some (Safeway) just strip the plus sign out without ever informing you, leaving you with an invalid email address in your account settings and, since you use your email to login, an invalid username as well.
Today I was surprised by a new response: a "helpful" employee went in and changed my email for me, thinking it was a typo.
You didn't receive an email with your decline notice and instructions to fix your [company-name] purchase because there was a typo in the email address you entered, specifically [my-email]@gmail.com (but with "[company-name]" written out in the address). I added the correct email address to your account...