AppleInsider is reporting that Macworld Expo 2008 in San Francisco will be when Apple unleashes its long-rumoured ultra-portable Mac.

The notoriously accurate rumour site describes the 13-inch aluminium sub-notebook at 50-percent light and strikingly similar in appearance to the current 15-inch MacBook Pro. THe unit is also said to have been stripped on an optical drive to keep the footprint small.

The sub-notebook will also reportedly be Apple’s first foray into using onboard NAND flash, the system will be the first Mac to take advantage of solid state storage to improve power efficiency and boot up speeds.

Apple is rumoured to be “gearing up” for a release in mid-January at the Macworld Expo and Conference which runs from the 15th through to the 18th.

In July of 2007 MacScoop claimed that “trusted sources” had passed on information that Apple is planning to release “a notebook that is so small and light that it could redefine the standards of ultra-portable computing.”

At the time the unit was tracking for an end of 2007 release.

Also, the Apple 2.0 blog is reporting on a client note from Gene Munster of the Piper Jaffray investment and finance company. The analyst is 75% certain that Apple will unveil an ultralight MacBook “or possibly an entirely new product” at the upcoming Macworld.