I made margarita ice cream using the recipe in Nigella Lawson's Forever Summer book. It was sublime. The most perfect texture of any ice cream/sorbet I have made so far. It froze beautifully after about 10 minutes of churning in my small machine. The custard base contains sweetened condensed milk and a combined 1/2 cup of tequila and triple sec.
More on adding alcohol to ice cream, as previously discussed with mzn and other chowhounds: I consulted my somehow previously overlooked Larousse Gastronomique and discovered a few tips when using alcohol in ice cream or sorbet. Folding whipped egg whites (stiff peaks) into the base will assist in freezing. There is also a recipe for "liquor ice" made simply by adding alcohol (6 tablespoons per about 4 cups) to sugar syrup and a squeeze of lemon juice then freezing it in the ice cream maker. There are some technical suggestions regarding the density of the sugar syrup...but imagine something like margaritas and mojitos made this way. As mzn suggested with his mojito ice cream, this would be a fabulous thing to serve in place of a cocktail to start a hot summer party. A little late, I know.