Chad White, Research Director for Smith-Harmon, published a great post yesterday on why image rendering is important for CAN-SPAM compliance. In it, he highlights an example email, where some sort of rendering issue results in the unsubscribe links and sender information to be white text on a white background. This makes the unsubscribe link totally unreadable, not legally compliant, and will probably cause an increase in spam complaints. YUCK.
I'm sure it wasn't intentional, but the company mentioned in the example email is doing something that bad guys have been doing for a long time: Obfuscating unsubscribe links and sender info. Hiding it in difficult to read colors or using images to try to encode it in a way to bypass certain kinds of spam filters. This is yet another example of, "if you don't want to be perceived as a bad guy, you need to stop doing what bad guys do."