Macscoop/MacOSXRumors claims that Apple is finishing development on a 12" MacBook Pro described as "ultra-thin":
The new laptop should be even thinner and weigh less than the current models in the MacBook Pro line-up. In spite of this very tiny and lightweight form-factor, the miniaturized MacBook Pro should keep its built-in optical drive and sport a dual-core processor, providing unequalled size/performance ratio in the PC industry, sources told MacScoop.
This "ultra-portable" MacBook Pro is estimated to be priced in the $1700-$1800 range and sport a 12" widescreen display.
The introduction of 12" MacBook Pro would fill a gap left by the 12" PowerBook model, which was dropped during the transition to Intel in early 2006. Apple retooled their laptop models which previously offered 12" / 14" iBooks and 12" / 15" / 17" PowerBooks to a lineup with 13" MacBooks and 15" / 17" MacBook Pros.
One analyst made similar claims in mid-2006. At that time, analyst Benjamin Reitzes stated that Apple was working on an "ultra-portable PC" to be delivered by Macworld San Francisco 2007. Reitzes included comments about incorporating the use of NAND Flash memory to speed up boot times. This concept of Flash-based latops was revisited in September 2006 by Appleinsider -- with expectations that NAND flash would make their way into the next revision of MacBooks due in 2007. While these rumors line up with each other, MacScoop makes no mention of Flash memory in this upcoming "ultra-thin" laptop.
MacScoop/MacOSXRumors cites "reliable" sources for this report and has had a recent history of some accurate reports with predictions of 23" (24") iMacs as well as Leopard info pre-WWDC.