I agree with Dekka, some "human" foods are very healthy for dogs. I regularly feed plain yogurt (good for digestive system and immune system, especially helpful for dogs who are prone to yeast infections and ear infections); raw veggies such as carrots, broccoli, green beans, etc.; and meats such as chicken, beef, turkey, fish, eggs, etc. Many people feed exclusively "human" food that they prepare themselves, which lowers the risk of food allergies and is usually more healthy (if you know what you're doing).
Foods that are harmful for dogs: chocolate, onions, grapes, rasins. You also want to stay away from foods with a lot of sugar (raw fruits are ok, but candy is not) or salt (one or two potato chips or french fries on a special occasion is ok, but really not healthy).
I think the reason why people get all bent up over feeding "people food" to dogs is because they think it will cause begging at the dinner table. But if you feed the food only in their bowl or as treats, they will not beg for it any more than they will beg for their regular food.