Every couple of years someone pops their head above the parapet, yells 'Mac Tablet' and then lets the rumour storm commence. Now the Mac Tablet is apparently back on the agenda - only this time it could actually be true.

An Asus insider reckons his company is already working with Apple on a tablet PC, which could debut as early as Macworld Expo 2008 in January. Asus certainly has form - it's one of Apple's contract manufacturers, churning out MacBook laptops and other devices.

The Mac Tablet is said to have a different form factor from other Asus designs, possibly harking back to a patent Apple applied for back in 2005. It's also said to run on the Intel Menlow / Silverthorne platform which has a form factor around 1.5 times the size of the iPhone.

The big question is: why would Apple put out a Mac tablet now?

Multi-touch

Tablet PCs have always been a very niche product, of interest only to 'corridor warriors', medics and other workers who need to write with a stylus on a touchscreen rather than use a notebook keyboard.

Apple doesn't seem particularly interested in any of these 'markets', so making a Tablet PC - as it has been traditionally perceived - just doesn't make sense. There's nothing in it for Apple. There's barely anything in it for HP, Acer or Microsoft.

But think about it: Apple has a multi-touch interface and it now has Cover Flow, Stacks and Spaces in Mac OS X 10.5 Leopard - all of which lend themselves to a touch-based interface. Mac OS X 10.2 Jaguar even featured handwriting recognition technology from Apple called Inkwell.

Ultra-portable

Then there is the perceived need for a Mac ultra-portable, especially since Apple killed off the 12-inch PowerBook in 2006. The smallest notebook in Apple's current line-up is the 13.3-inch widescreen MacBook.

Heck there are even a few Mac users out there who still hanker after an Apple Newton - the world's first PDA.

Then there's the Ultra-Mobile PC (or UMPC). Reaction to this Microsoft / Intel offering has been lukewarm at best. The form factor's OK, but the user interface is horrible. A Mac Tablet would be the UMPC 'done right'. The desire is there, the technology's almost there, but somehow we just don't buy it.

Apple already has an ultra-portable Mac. It's called the iPhone. And you can buy it this Friday.