Registration company Eventbrite have published a list of ten things that event managers can never get right for all their delegates.
These are the level of the content, the amount of activity, the amount (or not) of communication, the location, the price, the catering, the starting/finishing times, the number of delegates, the volume of the AV and the temperature in the room.
Another, remembered by the writer was his idea of putting tables in the middle of the exhibition area stacked with brochures from the exhibitors that visitors (their buyers) could pick up. Most exhibitors were grateful for the extra exposure but one complained that visitors were able to take his brochures without coming to his stand. Fair point or nit-pick?