I was at a show once, whereby one of the demonstration rooms were running 30 minute demo's, which isn't a bad idea in theory.
Trouble was, it was a very high end system, which was simply to much for these sensitive ears to listen to for 30 minutes.
Indeed, 3 minutes was enough.
What was funny though, when I got up to leave, there were several guys on the door who had locked it, and consequently I felt obliged to stay to the end.
Quite an intimidating experience really, but I guess people were enjoying themselves in the room