Um, two of my photos made with the Olympus E-1 (5Mpixel FourThirds sensor, same format as Micro-FourThirds) and printed 20x24 inch image area took awards at a juried exhibition hosted by the Center for Fine Art Photography.
The camera that Steve Huff and several other rating places have given camera of the year to is the Olympus E-M1, not E-P1 (which was the first Olympus Pen digital camera circa 2008). With the E-M1 and its super clean, 16Mpixel sensor, I could do even better on technical quality than with the E-1.
APS-C and FourThirds/Micro-FourThirds sensor formats are not that different in size. Typical APS-C sensor (nikon, pentax, sony) is ~16x24mm, FourThirds format is 13x17.3 mm. If you crop that APS-C to reflect the same 3:4 format, it would be 16x21.3mm vs 13x17.3mm. Canon APS-C is even closer (native format about 15x22mm).
But ... Care more about content and expression than "IQ/resolution": it gets you much further in photography than details of sensor size and megapixels resolution. ;-)
G