Iced coffee remains popular -- even at this time of the year.  Nearly 85-percent of the respondents in a new Dunkin Donuts poll say they're drinking more iced coffee now than they did last winter.  The majority is also turning to the beverage for more than just a treat. More than three-quarters think iced coffee enables them to be more productive at work, and 64-percent believe that by drinking iced coffee they have a "mental edge" over their co-workers.  Over half of those polled also credit iced coffee with giving them an edge on the social scene.  Overall, 55-percent admit they "feel cooler and trendier" when they have a cup of iced coffee in their hands, while 60-percent of adults under the age of 25 believe iced coffee contributes a "hip" factor to their image