My brother went to one of Tufte's seminars so many years ago I don't even remember when it was (must have been college for me, so over 5 years). At the time my brother brought it to my attention because of Tufte's presentation on the Challenger accident (which I assume he's still using), but now that I work at an institution where we seem to live and die by presentations (really PowerPoint to be more specific) it's probably good I was exposed to the concepts so long ago. I'm a big proponent of communication skills and being able to convey technical details, but unfortunately all my skill really comes from experience (so it feels more like an art) rather than documented best practices...

That's a rambling response, but in any case... Good luck with improving your data presentations!