In an extremely gutsy, if not crazy, move, the organizers of the Virginia Society of Healthcare The Experience Economist, they set up two check-in desks. One was manned by uninterested, unhelpful, surly people, and the other with folks who were knowledgeable, helpful, and nice. The results, predictably, showed that even just 30 seconds with the bad desk left a lasting bad impression of the whole experience.
This should be a "well, duh" experiment, if it weren't for the fact that so many registration desks are manned by those who don't make a great impression. Pay attention to your first line of contact, train them and treat them well, because they can set the tone for an attendee's entire experience with your meeting. It amazes me how often we forget that.
(Thanks to Ben at Certified Association Executive for the pointer.)