I have mentioned ggplot2 before but this item caught my eye because of its skillful use with a map of cycle tours of London.
Not that I intend to take a cycle tour of London any time soon but it occurs to me that creating maps to resturants, entertainment, etc., from conference sites would be a good use of it. Coupled with a topic map, as the conference progresses, reviews/tweets about those locations could become available to other participants.
Other geographic locations/information could be plotted as well.