It appears the Federal CAN SPAM Act along with email filtering is working reasonably well to reduce the amount of spam we all experience. If you are considering an email campaign using Constant Contact, MailChimp or any of the many services available, you'll want to take special steps with the copy you deliver to your customer and prospect inboxes to assure compliance with CAN SPAM.
Your list needs to be a clean, opted-in list. Your subject line and copy need to be crafted carefully. Your email layout needs to be "mobile device friendly," especially because a growing number of people access the web from a mobile device.