On April 29th I published a post about re-sending your email to people that didn't open it the first time. Well, mouse2house, an online retailer providing digital imaging products to the UK market, actually tried it out.
Their promotion was broadcast to the entire database, and then following
a three week delay, the promotion was resent to all recipients who had not opened the email -- and with some very good results: across both sends, the newsletter generated a 35% increase in sales from existing customers. Of these all the orders, 31% of them were generated by the second send. View the complete results here.
You can read the extended case study on MarketingSherpa (open access until December 18th).
I agree with MarketingSherpa's comments at the bottom of the article: a lot of email clients (Gmail, Outlook 2003, Outlook Express, Lotus Notes...) are blocking images and if the user doesn't download the images, there is no way of knowing if they opened the email or not. So if you would like to apply this tactic, please do so with caution. You don't want to be perceived as a spammer.