We were highlighted briefly in the Express last summer about cold-brewed iced coffee, and then the Post followed up with an article, quoting awesome food scientist Harold McGee on the flavor marriage of milk and coffee; also highlighted was the cold espresso-based drink the "shakerato" (which for you oldschoolers-- we actually used to serve at MTC).
Also mentioned was an incident with a now-defunct coffeeshop where a customer was refused espresso over ice (and threatened, via a blog post, with a very specific form of punishment) because the establishment wouldn't serve a coffee beverage where the form/quality of the espresso was compromised.
Why all the hullabaloo? Coffee beans for espresso are roasted and blended to preserve unique flavors that bloom under the intense pressure and temperature of the espresso machine. When that hot, concentrated shot of liquid is shocked with ice, it tastes completely different than the fragrant, savory, sweet, and creamy treat that it was meant to be. Most of us agree that taste is well, bad. We also don't like to see those carefully roasted espresso beans covered up in a drink with tons of milk and most likely, sugar.
Lurking in the background is another reason why some people have been known to order espresso over ice-- they simply use the "free" self-serve condiment milk to fill the rest of the cup up, essentially making their own iced latte for the cost of just ordering a regular espresso. There's even a pejorative term for it, but I don't like to use it. One can understand the motivation behind this-- but considering that vast majority of people only use 1-2 ounces of milk in their coffee, someone taking 8-10 ounces of milk for their on-the-sly iced latte cuts into the bottom line of a business. At our store, the additional dollar you pay for the iced latte vs. a double espresso accounts for the milk, the ice, and the barista pre-mixing it for you.
Cold-brewed coffee tastes completely different than say, hot-brewed coffee that is just leftover and then stuck in the fridge until cold. It can be enjoyed on its own, or with a little bit of milk or simple syrup (sugar that has been pre-dissolved in water) to enhance the natural flavors. If you like your espresso unaltered or like to drink regular hot coffee black, you'll probably find cold-brewed coffee a refreshing, flavor-packed substitute when you need a cold jolt on a hot day. And if you usually drink iced lattes, try iced coffee with milk-- you will be surprised of the flavor difference.
For the record, there are some specific methods out there for brewing coffee directly over ice to actually capture flavors at the point of chilling-- notably the Japanese method, which uses a pour-over brewing style, filtering the concentrated coffee directly onto ice cubes; or Vietnamese-style iced coffee, which brews a single serving of coffee over ice and sweetened condensed milk.