actually, if you drink coffee then exercise, it increases the ammount of fat burnt.
http://www.nutros.com/nsr-0202k.html

So it doesn't really lower your metabolism. And, it does suppress your appetite. It also improves mental alertness in men, enhances your sexual drive etc. And Most doctors suggest that up to three cups a day of coffee for an adult (assuming they aren't pregnant etc) can be consumed without any negative reactions.