I know the some of the bads: images turned off, fails; too many attachments, goes to SPAM. Maybe that's enough.
But I see them in my inbox all the time with maybe two or three slices as click through URLs.
So I built a beautiful, long (client text), stylized 600px wide image in Photoshop with cool pictures, stylized text and colored backgrounds everywhere. Sliced it up and stacked it up. No surprise, it doesn't work everywhere.
What is this forums thoughts? Like I said, I see them on behalf of large corporate clients, targeting me with theor product. It's clean. No CSS to worry about.
Just read Image Blocking section.