Vinegar is great, and is a wonderful alternative to high-fat and high-calorie dressings. Balsamic Vinegar has the highest sugar content of all the vinegars, so keep that in mind if it is something you are sensitive to -- it is natural sugar, though, so don't be too paranoid.
From About.com: "Although it is considered a wine vinegar, it is not a wine vinegar at all. It is not made from wine , but from grape pressings that have never been permitted to ferment into wine.
Sweet white Trebbiano grape pressings are boiled down to a dark syrup and then aged under rigid restrictions. The syrup is placed into oaken kegs, along with a vinegar "mother," and begins the aging process. Over the years it graduates to smaller and smaller kegs made of chestnut, cherrywood, ash, mulberry, and juniper until it is ready for sale. All of these woods progressively add character to the vinegar. As it ages, moisture evaporates out, further thickening the vinegar and concentrating the flavor.
Some balsamic vinegars have been aged for over 100 years. It is this aging process that makes true balsamic vinegar from Modena in Northern Italy so expensive. Luckily, a little balsamic vinegar goes a long way."View Thread