Here's an interesting stat. This client hired me to write an email promo campaign. (He's done some throughout the year but hired me to write his copy this time.) The first one, he insisted, was a long copy HTML email. Results? Not bad ... 80 sales for $8,000 profit (it's a $100 digital product).
This was late November last year.
But I finally convinced him to try a short copy plain text email "pushing" the reader to a long copy web page (salesletter) instead. The results? See for yourself...
http://SuccessDoctor.com/images/sales.gif
Total of $150,000+ in just 3 weeks.