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Opt-In Forms - What Data Should You Collect?
http://cdemails.com/articles/3477/1/Opt-In-Forms---What-Data-Should-You-Collect/Page1.html
VerticalResponse Blog
VerticalResponse, Inc. is a leading provider of self-service email marketing, survey and direct mail services empowering small businesses and non profit organizations to create, manage and analyze their own direct marketing campaigns.  
By VerticalResponse Blog
Published on 08/26/2008
 
The question about the "right amount of questions" to ask of people signing up to your opt-in form is a tough one to answer, we get it all the time. Then we have to give the lame answer "that depends." But it's true, it does depend. It depends on what you really need for your business. There are varying degrees of data collection methods, here I've attempted to outline a few.