Backpacker, me old china, back on page two you mentioned letting your have-a-go pax preform a loop....please don't!
In fact, I have upset some posters by insisting it is way out of order to frighten first time pax with aeros of any sort.
Mary, rest assured that I do not do this unexpectedly to first time passengers. I only do this on flights which are fully prepared and briefed as an aerobatics experience flight.
The passengers know that I'm going to fly aerobatics with them: That's what they're there for. For most of these passengers it's not their first flight in a light aircraft by far - some are even fully licensed pilots. I fully brief them with regards to nausea, G-forces and whatnot. In the air I brief each and every individual maneuver. The fact that I teach them to fly a loop properly at the end of the flight is a bonus - if they can handle it and want to try it. It usually takes them three tries to get it right.
My comment was directed more towards the earlier poster who said he would let his passengers (in a similar situation) perform a roll. As a roll requires a quite complex coordination between pitch and roll control (both for an aileron roll and a barrel roll), I think it's easier to teach passengers to fly a loop instead (which requires pitch control only).
(And I know that last statement is not quite true. Both maneuvers require pitch, yaw and roll control to some degree to come out right. But a reasonable approximation of a loop can be done with pitch only, as long as you don't mind a 30 degree course change. Not so for a roll.)