It depends on the school of thought you subscribe to. Some people say it encourages dominant behavior, so it's bad. Some people say that it's natural for dogs to sleep with their packmates, so it's good. You can pick your philosophy.
I will never forget the first time I dogsat for Thor. He slept in bed with me, and in the morning, he rolled over to get a tummy rub. He is very protective of his tummy and had never let me touch it before. Needless to say, this melted my heart and he has slept in my bed ever since!