The field of design is an ever expanding area with different interpretations of what it actually is. Personally I feel design is simply a user centred problem solving process, and the disparate nature of the area perpetuate the lack of a unified definition.
At the moment there is some great research being carried out by the Design Council in the UK. They have measured the value that design can bring to businesses and organisations which has produced some substantial results. Anyway these are just some quick thoughts, I will return to this topic at a later date :)