Apple Investigating Thinner Notebook Enclosures
A December 2006 patent application (published today) from Apple indicates they are working on thinner / stronger enclosures for their laptops.
Apple describes two conflicting design goals for producing thinner and lighter laptops: "the desirability of making the enclosure lighter and thinner, and the desirability of making the enclosure stronger and more rigid."
Instead, Apple describes an improved enclosure where the parts are "structurally bonded together" to form a singular composite structure. In the application, Apple acknowledges that while "current enclosure designs work well, in many instances it would be desirable to provide enclosures that are thinner, lighter, stronger and aesthetically more pleasing than current enclosure designs."