Over the history of cocktails, certain flavors have become trendy during particular years. First the cocktail was invented, then the "fancy" cocktail, then the "improved" cocktail. These variations added liqueurs like curacao, maraschino, and absinthe to the regular formula. In the early 1900's, grenadine was all the rage and suddenly you'd find a splash of it in all the drinks.
A hundred years later, the same thing happens and I run around and try to document it. In 2007 and 2008, what cocktail menu didn't suddenly have three drinks with St. Germain on it? We're currently seeing a revival in ginger flavored cocktails. And I believe that 2008 and 2009 will be known as the years of smoke.
Bartenders have taken different approaches to putting smoke into drinks. Sometimes, they light stuff on fire to make smoked Coke (Eben Freeman of Tailor), smoked ice (Daniel Shoemaker of Teardrop in Portland), and smoked syrup (Cody Robertson of San Francisco), and in a drink I just learned about, smoked strawberry shrub(!!!) with scotch and bitters at Absinthe.
Other bartenders add liquid smoke to drinks. An early version of this was in the (awful) Smoky Martini, a Martini with a rinse of scotch, and a (less awful) Martini with a smoke-brined olive inside. In the past couple of years though, it's been all about the rinse. Folks use a rinse of Islay scotch like Laphroaig or Ardbeg, and within the last year they've gone nuts for rinses of mezcal- especially in San Francisco. At Clock Bar they have a drink with Qi black tea liqueur for similar effect.
As bartenders and consumers get more fetishistic about smoke, it seems they're putting more of it into cocktails. It used to be bartenders would mix half mezcal or Islay scotch in a drink with half tequila or blended scotch so as not to overwhelm the drinker, as in the Carter Beats the Devil cocktail. Now you're more likely to get a full dose of smoke but tempered with robust mixers like pineapple gum syrup in the Single Village Fix.
Luckily I have a very trendy palate, and have been sucking down smoky cocktails like they're going out of style. And they will, of course, but hopefully not until sometime in mid-2010.