What makes a unibody Mac better than what came before?
The unibody design makes the case lighter and stronger. Since it is machined, there is minimal error in the creation of the case. For more information, watch the video on http://www.apple.com/macbookpro/design.html. The first unibody MacBook Pro was the 15" model released in 2008 and had a removable battery. I believe that all other unibody models (and only unibody models) have integrated, non-removable batteries.