What's in it for me?

If you want marketing, contact, or demographic information from people, give them a reason to give it. As Seth Godin found, people have become wary of hading over their information. They’re sick of being spammed, telemarketed, and junk mailed. Your customers know that when you ask for their mailing address, they’ll probably start getting catalogs from you.

Those catalogs are there for you, not for them. They don’t get any real value from the unwanted catalog, but you get a potential sale. If you want your customers to provide their email address, their marital status, or anything else, give them an incentive.

Are you running a marketing drive to find out the income level of your average shopper? At the end of your checkout process, after the customer has commited to making the purchase, tell them "You can get this order shipped for free if you complete this short survey."

Or maybe, "Thanks for your order. Tell 5 friends about us and we’ll take 5% the order total." Then give them a form that they can use to email their friends.

Your customer’s personal information is valuable. Don’t expect them to give it to you for free.