Our blogging-shy designer, Brian Willis, suggests this article on how Gmail treats images, as a suitable contribution here. It says basically that text will be more important than images as result:
Gmail strips out all graphics by default. You have to proactively turn them back on and do so on an email by email basis. This is going to dramatically effect how newsletter publishers embed their sponsor’s messages into the email since Gmail represents the email equivalent of TiVo, at least as far as ad skipping is concerned.
Read the article on eROI. Thank you Brian!