I love the one day writing workshop format. I've been giving these ("Break the Block"; Literary Travel Writing", "Flash Fiction" "Techniques of Fiction" & etc) for some years now at the Writers Center in Bethesda, Maryland, and also, lately, via Dancing Chiva in Mexico City. Why do I love it? Unlike an on-going workshop, a one day is much easier for me to fit into my travel-cluttered schedule, and I not only get more students, I get a more varied group. I've had many beginners, but also magazine editors, accomplished journalists, and many who've published books. So it keeps me sharp. And I love taking one day workshops myself--- it's a way to freshen up, get jolt of inspiration. At the Writers Center, I've taken, and warmly recommend, Khris Baxter's one day short screenplay writing workshop, Lindsay Reed Maines's yoga and writing one day workshop. And, though not a writing workshop, as I did find it extraordnarily helpful for my novel, I recommend Edward Tufte's splendid and entertaining one day course, Presenting Data and Information.
And two more recommendations: this fall, my amiga award-winning novelist, short story writer and essayist Leslie Pietrzyk will be offering two all-new one day workshops at the Writers Center, "Set Your Prose Free Through Collage" and "Flex Your Creative Muscles." Over at her blog, Work-in-Progress, she provides a full description of both.