Apple achieves the smooth and shiny finish of its products by manufacturing step called anodizing. The process makes metals like aluminum and titanium resistant to corrosion by growing an oxide layer into the metal. That’s right, they protect against corrosion by adding a layer of rust!
Anodizing, an electrolytic passivation process, basically increases the thickness of the oxide layer found on metal surfaces, such as the Unibody aluminum chassis of your MacBook Air or the iPod nano music player.
The process changes both the microscopic texture of the surface and the crystal structure of the metal near the surface. The end result of anodizing is a much stronger and mostly scratch resistant surface. Also providing better adhesion for paint primers and glues.
The shininess, is achieved with anodic films. Those typically have thick porous coatings that absorb dyes or thin transparent coatings that add effects to reflected light. Theoretically, Apple could play with the anodizing process and produce a shiny colored notebook chassis.
Below is a great clip based on a chapter in the book Eight Amazing Engineering Stories, it explains anodizing in easy to understand terms through the mouth of Bill Hammack the Engineer Guy.
Anodizing is used on various Apple products today, and will most likely be used on the upcoming iPhone 5, which is rumored to have a metal-clad backside. (Much like Bender on Futurama.)