There have been a number of blog posts recently discussing designing emails that look good and inspire clicks even when images are suppressed. Much of this is related to the EEC whitepaper showing that the majority of email users suppress images in emails and the 2008 email design guidelines published by Campaign Monitor.
I happen to be one of those cranky users who suppresses images by default, even in the emails with the cute bunny pictures. Up until about 3 years ago, I was using a mail reader that did not render images (or attachments). It is always interesting to me to watch how senders in general are reacting to the marketplace. Some senders have mail completely incomprehensible without images turned on. Their weekly (or more often!) email is a network of empty boxes on my screen.
For the most part, the emails are useless to me without images, and while I have occasionally loaded images or check the website, the emails are not that much better with images. I stay on the lists now as an informal study of how long it will take the sender to notice I have not opened, clicked or purchased from their emails.