I think Jaymie's questions above are great! I would just add a question to the workshop leader about whether the lesson was too long, too short, or just right for the classtime. And then file away responses so that in 4/5/6 years when we come back to that same lesson, we can make needed adjustments. (I can barely remember two weeks later what the lesson was and what did or did not work......)
And we plan to call workshop leaders/shepherds to thank them and for feedback midweek while lesson/rotation is still fresh in their minds (past experience with written surveys - amazingly low response rate).