If you’re going to put the comment “Make your emails look good, perform better” in your pre-header, it probably pays to make them look good without images enabled too.
Bit of a noob mistake from Campaign Monitor, but typical of companies that whilst offering a great service – hey, we use it for some clients – don’t really get email marketing.
Alt tags, people. Alt tags. Easy to use, easy to format. Kick-butt in the readability stakes.