I'm a firm believer in having as much information as possible about my training attendees, as soon as possible. This simple exercise, used as part of the introductions, will tell the trainer a lot about what will work and not work for each of the participants.
Ideal Group Size
Less than 20 or the process is too slow and cumbersome
Time For Exercise
Expectations for the day
Detailed Instructions If Needed
Incorporate this into any introductions you do at the start. Ask each person to complete the following:
The last thing I want to hear today is....
Go around the room, having each person introduce him/herself and explaining how they answered and why.
Reassure if necessary that they won't be disappointed or explain why they might experience something that's useful but may fit in their discomfort zone.