When unfulfilled Apple rumors don't die, there's usually a good reason. Having moved on from the iPhone, the tech rumor mill is now churning up new whispers of a game-changing Apple product: an ultra-thin MacBook. Ultra-thin laptops are nothing new. So why should we care?

Apple traditionally makes quick changes in its product lines; even seminal product re-designs happen inside of 18 months or a year. But when it takes the Cupertino-based company more than a year and a half to launch a product, it's either dead in the water, or deadly to the competition. It took nearly a decade of development for Apple to launch the first OS X. The iPod was a multi-year endeavor, and the iPhone took so long to develop that it developed an almost mythical aura in the tech community. We've been hearing about ultra-thin MacBooks for close to three years now, which means that if and when it arrives at the MacWorld conference in January, it will be a device that leaves other laptop makers scrambling. With the dearth of solid information that accompanies these rumors, I'll put my tech-spertise on the line to predict what we'll see in the ultra-thin MacBook.

What We (Think We ) Know

The rumors I've read make some logical predictions based on trickle down technology from the MacBook Pros. Like the MacBook Pro, the ultra-thin machine will have an LED (or OLED) screen, instead of the traditionally-backlit screen, to save power. That's a no-brainer. It will also probably have a 13-inch screen, ala MacBook, because 13 inches is a good compromise between screen real estate and weight/footprint. Let's go from there.

What I (Think I) Know

Some rumors describe the ultra-thin MacBook as lacking an optical drive, while others consider that option an absurdity. I think the elimination of optical drives is as much an inevitability as was the elimination of floppies; with Internet and wireless technology improving as quickly as it has, tangible media are becoming quickly obsolete. However, the machine will have to come with an external SuperDrive, if only because it's currently impossible to do OS upgrades with anything but a DVD. Maybe OS 10.6 will arrive in USB flash-drive form, but until that (and all software) moves away from discs, the drive isn't dead -- yet.

I'm also predicting built in Wi-Fi as well as built in AT&T wireless broadband. The machine won't have a PCMCIA slot, as the MacBooks don't, so they won't be able to take advantage of wireless broadband cards. Since Apple already has a relationship with AT&T because of the iPhone, they'd be stupid not to include wireless broadband functionality in this machine -- especially since it's an ultra-mobile machine meant for people on the road.

How about the guts? It'll have the same 2.6 Ghz Core 2 Duo chips as the MacBook, but will also have all NAND flash memory. That's right: no hard drive, and no moving parts. This will limit the capacity of the machine; its total storage will probably max out at 40 or 50GB, simply because the inclusion of any more flash memory will be a cost-prohibitive (though possibly built-to-order) feature, but it will allow for near-instant boot times. This hardware profile will position the ultra-thin MacBook above the regular MacBook in Apple's price scale, but below the lowest-level MacBook Pro. It will be in an aluminum enclosure, like the MacBook Pro.

Now for the fun stuff: the groundless speculation. Since the machine is built to be mobile, I'll be expecting a redesigned AC power adaptor with an extra-light body and extra-long, airport-friendly cable. The machine will be only as big as the screen requires: .5" thick, 13.1" wide, and 7" deep, weighing in at about 2.5 pounds. It will include a portable DVD-R drive and possibly even a built-in iPod/iPhone dock to reduce the cable clutter in your computer bag. It might even sport a modified version of OS X that runs a basic-feature mode much like FrontRow provides a basic media mode: a simple, resource-light GUI that gives you immediate access to e-mail, Address Book, iCal, Dashboard and iWork. Look also for enhanced multitouch capabilities on the trackpad, which could allow for the quick and easy manipulation of files and desktop space.

While Apple certainly won't be the first to do a super-slick UMPC, they might just do it better than anyone has so far. And even if American buyers aren't clamoring for yet another small laptop, an ultra-thin MacBook has the potential to bolster Apple's weak presence in Japan, where tiny electronics are adored (if not fetishized). Whatever Apple's reason for introducing the new Mac, Apple devotees should put January 15 on their calendars, and be prepared for something very, very cool.