I've been a long-time customer of Netflix (www.netflix.com), a DVD-rental company. If you don't know the company, they are worth checking out. They are a rocket-ship success story. Their astounding success is attributable to one thing: they are fundamentally changing the way video rental works. Rather than forcing me to get in the car and go to a video rental store, they mail me the DVDs I want to watch. Even better, they allow me to keep the DVDs as long as I want, restricting only the number of DVDs I can have out simultaneously (e.g., I always have two at a time but can keep any particular one as long as I like).
I recently received a great viral message from them. It had everything you'd want: solid, creative design visually showing the benefits of their offering, a strong promotion of one month free, an easy call to action, and clearly written copy (although it was a bit long). Interestingly, Netflix did not provide a forward option within the email, but instead relied upon me hitting the forward button on my email program.
Because I'm a huge fan of Netflix, and believe others would be as well, I forwarded it the old-fashioned way to lots of people. Interestingly, as a consumer, it felt just a little more personal to press "forward" on Outlook rather than using a built-in form from Netflix. I am going to contact them and find out how this performed and what, if anything, they may have learned from this valuable campaign.