Just finished listening to a great podcast on card design by MaRo. He revisits earlier articles written about the subject: "why does WotC design bad cards?"
While MaRo has a voice that I find quite unpleasant, nasal and almost overly geek with a slight slur, and the fact that he is recording while driving to work, the subject is very interesting. I recommend checking it out if you ever wondered why bad cards exist.
http://magic.wizards.com/en/articles/media/podcasts for the podcast, #279, or just google: "when cards go bad" for the articles.