i had to design an e-dm for a client in insurance field and send them over a .jpg to approve the layout (after that the sitebuilders would cut it and make an html e-mail and send it over to their clients)
the first comment was:
"we like the layout, but there's a serious issue: if we click on the links, nothing happens"
oh, and they found a couple of typos as well, which had to be corrected instantly. well, i just copy-pasted the text from their e-mail :)