I really love the comparison between the CTA/Pitch of Zumbox compared to EarthClassMail.com. EarthClassMail is also not free, and also is far to involved to get me to be excited and sign up.
Zumbox offer a new marketing approach. They try to get people to sign up and try to get marketers to send mail to those who registered. I guess their ultimate goal is to render the USPS worthless.