This expression might sound strange to someone who doesn't speak English as his native language, as in, 'How can a person be more than happy?' It is usually used in connection with an activity in which a person would engage, such as in, 'I would be more than happy to clean that for you,' or 'I was more than happy to go to the theater with him yesterday.' Occasionally the expression is used in other ways, such as in, 'We are more than happy with our new house.'