Appleinsider provides additional confirmation that Apple is indeed working on a sub-notebook version of their MacBook line.
The rumor site draws parallels to Apple's PowerBook Duo, Apple's first sub-notebook released in 1992. The Duo-line of PowerBooks offered a unique 152-pin port in the back that allowed it to connect to various Docks that provided additional functionality, such as external drives, video capabilities, and ethernet that were left off the notebook itself to maximize portability.
Appleinsider reports that the new mini MacBook will be "lighter and more compact than any other Mac portable Apple has put forth in recent years" and is on track for release near WWDC in mid 2007. Other features listed in the MacBook include the use of NAND flash ram to speed up boot times, as well as the exclusion of an optical drive to save on space.
The first rumors of a sub-compact ("Ultra-thin") notebook coming from Apple came in December 2006 from MacScoop. At that time, however, the rumors pointed to a MacBook Pro model that would see miniaturization with a 12" Widescreen display. It isn't clear if these two reports are related , and this new report may represent a distinct project.
A patent application from January provided additional evidence that Apple had been actively working on methods to miniaturize their notebooks, with research into alternative locations for the optical drive in a laptop computer. Making smaller laptops was listed as the motivation for pursuing these alternative designs.