(Above: the 202 x 205 mm, i.e. ~8 x 8 inches, Canon CMOS sensor (Left) Vs a 135 CMOS sensor (Right) - The 135 "Full Frame" sensor just looks like a dwarf in comparison!)
via http://dc.watch.impress.co.jp/docs/news/20110915_477641.html
(Excite English Translation Here)
It is told that this new super large Canon CMOS sensor is of very high sensitivity that it can record the image of a shooting star at lightness/brightness level as low and as dim as 10th magnitude for an example work as below:-
Just for information, human eyes can see stars as dim as 6th magnitude at best and thus this sensor see much much things in the deep sky than we human do. Do note that the star brightness magnitude is of the same scale as EV steps of which each grade is of double/half of the brightness against the adjacent grades.
Some Pentaxians would then think that we have the 645D that has a "much" larger sensor. In particular, this is the official comparison:-
via http://www.pentax.jp/japan/products/645d/feature_1.html
So, as we can see, the 645D sensor is actually not that much larger after all.