I agree with the point Leanne mentioned: The tone of the prompt that goes out would elicit responses in the same tone.
I just read through Norma's post on "Things that Go Hmmm? and loved how she positioned the prompt as talking to me personally. I think by mentioning some more personal details of the course and connecting the prompt to the participants would produce some fantastic responses.
Something like, "We've got a great group of 24 members located throughout Canada and Europe in the Health Care Quality Improvement program........ then tell me more stories about the course. Then I would reply with my story.