This one is a total surprise to me. I thought I had heard of all techniques for 3D printing - until today, when I read Deelip Menezes' blog, where he pointed out Ireland-based Mcor Technologies. They make a 3D printer that uses paper as media:
The Mcor Matrix desk top modeler can produce ready to use, three dimensional models from standard A4/Letter paper. This cost effective model maker will enable students, designers, engineers and hobbyists create 3D models at 2D prices.
Mcor provides specialized software that renders 3D objects into "slices" suitable for sending to the printer. The software even identifies and models the necessary support structures used temporarily during printing. Standard paper sheets are glued together during the printing process to form the 3D structure, using a "patented selective adhesive system."
Mcor claims the Matrix printer operations at "up to 40 times less expensive" than traditional 3D printers, since you can use typical A4 paper such as you can easily find at your neighborhood office supply store. The printer is not cheap; for its 1Q2008 Ireland and UK introduction, the projected price is €15,000 - 18,900 (USD22,000 - 28,000), but the media certainly will be a lot less expensive than that of their competitors ("the cost of the build material is 0.01 euros per cubic centimetre".)
Depending on the amount you intend on printing, this device might end up being less expensive to use than the highly-anticipated Desktop Factory USD5,000 (or €3,400) 3D printer. Desktop Factory says "The cost of the build material is expected to be about $1 per cubic inch." Translating the DesktopFactory media price to euros, my rough arithmetic tells me that its media cost is €0.0415 per cubic centimetre, or 4.15x as expensive as Mcor's.
This means that the the Mcor Matrix could become less expensive than the DesktopFactory after printing some 370,000 cubic centimetres worth of 3D objects, since you're saving around €0.03 per cubic centimetre. How much is that? Approximately 370 litres, or about 600-800 hand-sized objects, or a print per day for two or three years.
This technology tells me one certain fact: 3D printing is still in its infancy and there are many paths it may take. Great idea, Mcor!