AppleInsider has learned that Apple is set for a major redesign of their MacBook and MacBook Pro notebook lines.

The 13-inch Apple MacBook computers are supposed to see the biggest change. The MacBook is supposed to get a new aircraft-grade aluminum and stainless steel case instead of the eco-killing plastic casing.

The MacBook Pro is also supposed to see changes in its design, possibly adopting some elements of the MacBook Air.
Of course this is just a rumor at this point, but Apple Insider did a great job at capturing the life-cycles of the Apple notebooks with a nice flow-chart. More details on AppleInsider.