Sake is a type of alcoholic beverage with origins in East Asia. It is typically associated with Japan, although it may be based on Chinese cuisine. Regardless of historic origins, Sake is a Japanese beverage and is associated with (if not brewed in) Japan.
Sake is fermented, like wine or beer, and is based on short-grain Japonic rice. "Junmai" sake (or expensive sake in general) is equivalent to fine wine or quality wine, whereas other sake is equivalent to table wine or generic wine. The more generic kind can be found in many liquor/wine stores in the US (most common brands include Fuki and Gekkeikan); higher quality kinds may only be found in more cosmopolitan liquor stores.
While sake is typically associated with heat, it can be served at a variety of temperatures. Most sake--i.e. the kind you will find in the U.S., or at least the kind that will not seem to be outrageously expensive, is best when heated (which, by the way, increases the effect of the alcohol--more drunkenness for less liquid! :dance:). Place about 1/2 liter of sake in a microwaveable cup and microwave it for 45-60 seconds (less if you have a freakishly powerful microwave, ~1200 watts or more) for a heated, wonderfully tasty drink that is enjoyable any time. While heated sake is more common in the winter, do not be afraid to enjoy heated sake in the summer--I'm drunk off heated sake right now! It's awesome.
Sake can also be served chilled, and sake connoisseurs may insist that sake should be served chilled. It is true that some sake (perhaps mostly the most expensive/high quality sake) is better when served chilled, and if you are going to a high-class sake bar in Japan, it may be better to ask for chilled sake. Otherwise, don't be afraid to heat your sake.
Room temperature sake is acceptable, and is probably more tolerable than other alcoholic drinks, but serving sake heated, chilled, or in a cocktail are all better than simply serving it room tempeurature. It is also worth noting that sake should be stored in the fridge (or another cool, dark place) and consumed quickly after opening. Unlike much other booze, sake is not a lot better when aged--just drink it, ya mook.
Heating can be achieved by either microwave (described earlier) or double-boiler. For double-boiling: - Pour the sake into an earthenware vessel (i.e. what you would get with a sake kit--I just use the microwave :eng101:) - Heat a pot of water on the stove (preferably not boiling) - Place the vessel in the pot of water - Heat until the sake is ~105-110 degrees (use a thermometer :science: )
Some note that there's a difference between microwaved sake and double-boiled sake, but you really have to search for it to notice it.
Sake is a fundamental component of many Japanese sauces, including the ubiquitous Teriyaki sauce (which uses sake, sugar, rice vinegar, and soy sauce). Sake may be replaced by Mirin, which is a sweetened sake with less alcohol and may be sold like cooking wine.