Come on people... 3 people complaining about what they claim is an incorrect sensor size due to one other magazine article. All the additional research I am finding shows that the dpreview article is incorrect with their size.
Articles at:
http://www.gizmag.com/canon-120-megapixel-cmos-sensor/16128/
and
http://www.wired.com/gadgetlab/2010/08/canon-120-megapixel-sensor/
both support Tom's reported size. Even the photographs indicate it is rectangular, not square like the dpreview measurement would be.
Finally, use some common sense on the measurement. How big is 200 mm in an understandable measurement? It's about 10 inches square, so about the size of a piece of notebook paper! Everything I read points to an error in dpreview, not Tom's.