A friend recently gave me a small jar of asafoetida without telling me how to use it (or that it smelled horrible). In my googling, all I've been able to find out so far is that it's the dried sap of a Middle Eastern herb, used as a natural remedy, should be stored in a tightly sealed container due to its strong scent, and should be used "sparingly." I'm interested in knowing more specifically how I might use it in cooking (and if its flavor is better than its scent). 
It is used extensively in Indian cooking. I have one book, Lord Krishna's Cuisine that calls for it in virtually every recipe, and each time reminds you to cut the amount down by 3/4's if you can't find Yellow Cobra brand. It does indeed have a flavor someone reminiscent of aged garlic. It is thought to have medicinal value as well (see the wikipedia article for details). 