Interesting read. Will peruse more in-depth later...
I like the experiments that are mentioned in the article. What I'm kind of interested in is what commonalities exist between synesthetes. Is E-flat pine green for most of them? Is the number seven always red? Is there a gender factor creating splits in commonalities? From those common reported experiences you can then see more about how synesthetes are differently wired and, of course, how the brain is wired in the first place (processing, filtering, recognition, storage etc.) Someone get on this post haste!