It’s even more complex than I thought initially. It’s not that you cannot put Lithium batteries in your hand luggage if you fly by plane starting 1st of January, 2008. It’s quite the opposite: They don’t want your spare batteries in checked luggage. “Spare batteries” means batteries that are not attached to a device (camera, computer or else). Spare batteries are prefered in hand-luggage.
It makes even less sense to me. And it will be awfully difficult to enforce. But try and make things clear at check-in to decide what to do with your spare batteries when traveling by air.