What is chartreuse good for
Chartreuse is an herbal French liqueur that comes in a 2 colors: yellow is smoother and green is more alcoholic and pungent. Here's a refreshing looking recipe for a Chartreuse Swizzle from Serious Eats: http://bit.ly/dW5YkP but I've also seen it used to spike hot chocolate! Pretty versatile, and worth experimenting with.
Chartreuse--the only color named for a liqueur! Green Chartreuse is made according to a secret recipe from 132 plants--that's probably enough to tell you that it's in the category of herby liqueurs. I like it by itself as an after-dinner drink, but it's an acquired taste. It's an amazing addition to a standard martini: coat the glass with a little Chartreuse, and pour out the excess before proceeding with the rest of the drink.
One of my favorite rabbit recipes is flamed with Chartreuse. If you used chicken instead, you'd basically follow a coq au vin recipe, substituting the Chartreuse for the Cognac or Armagnac.
Chartreuse is also a delicious (some might say interesting) flavoring for ice cream.
The Chartreuse region in France is really fun to visit. Although Chartreuse is made in a factory, it's made by Carthusian monks, an order that otherwise spends their time in silent prayer. Only two monks at a time know the exact formula for the mix. You can tour both the factory (yes, they give samples) and the monastery.
Sipping a bit slowly after dinner!
I use it for a martini kind of thing. Use a very flowery gin such as Bombay and add just a dribble of Chartreuse. Shake in cocktail shaker over ice and drink it neat and icy cold. The color is exquisite, like the earliest tenderest spring leaves, and the fragrance bewitching. We call this a Chanteuse, or less appetizingly, an Irish Spring.