I love Bill's line of thought: "The real secret to email marketing has nothing to do with deliverability, rendering, or any number of other technical issues we discuss to take our minds off our dwindling response rates. The real secret has to do with Creative. What are you sending to the customers that you reach to make them want your message in the first place? Not only want it, but desire it?"
He then goes on to give some examples (including images) of some welcome letters which do it right and go towards building a rewarding relationship with their subscribers..
Read Bill's article: http://email.dma.org.uk/_Attachments/Resources/4388_S4.html