Something that worries me a little after seeing the PAX demo is the new system of cities exporting food and production to other needing cities. I did not see any sign of the exported food or production having any cost, or counterpart. I hope that is not the case, Civ5 already suffers to some extent from the "instant gratification" generation problem; that is, many things do not have a trade off, a counterpart, a cost of opportunity. I would like to see the new mechanism as a zero sum option, meaning that the city that exports 4 food units also looses those 4 food units, and not that the 4 food units are a magical product of the caravan. Did anyone see a sign that this is indeed the case?