Steve Jobs, CEO of Apple Inc. unveiled the world's thinnest laptop, MacBook Air (pictured here, via), during his keynote speech on the MacWorld 2008. Accoridng to PC Advisor, MacBook Air is 0.76 to 0.16 inches thick, back to front. It's so thin that it can fit inside a manila envelope.
Update: More info from Truemors:
MacBook Air, an ultra-thin notebook that features a 13.3″ widescreen display, built-in iSight, 80GB hard disk standard, 1.6 GHz standard, 45 Watt MagSafe, 1 USB 2.0 port, Micro-DVI an LED backlight, 5-hour battery life, multi-touch trackpad and a Core 2 Duo Processor that Intel shrunk 60 percent. The mini processor measures as thick as a nickel and as wide as a dime, but will certainly cost a pretty penny. The latest MacBook lacks an optical drive, but Apple will offer a Superdirve accessory for $99. .... and the price tag? $1799.