Apple has been using a lot of aluminum in its iPhone and iPod devices for years now. The problem with aluminum is that it blocks radio signals making wireless syncing difficult to do. Apple gets around those issues today by putting the wireless hardware that needs to send and receive signals behind plastic of some sort.
Recently Apple hired a Senior Composites Engineer named Kevin Kenny that previously worked for a company that used carbon fiber to make bikes. This fact has led many including Cult of Mac into believing Apple is hard at work on iPods and other device with carbon fiber cases. They reckon that for wireless sync to come to the iPod line these carbon fiber cases are needed for good radio signal transmission.
The rub as Fast Company points out is that carbon fiber blocks radio signals as well. That means that any gains from moving to a carbon fiber case for the devices would potentially be no better than using a new aluminum case design. The other trade off with carbon fiber is that the material is very expensive and more difficult to work with than aluminum. So who's right? My money says that the new composites engineer may have a lot of experience with carbon fiber, but I am sure he knows his way around other materials too. I don't see the cost of carbon fiber being something that would make for an appealing price on an iPod or tablet at this point. I do know that a carbon fiber iPad would be dead sexy.