So far, i've tried 4 different DSLR camera systems.. Olympus (E520, E30), Pentax (K20), Canon (40D) & Panasonic (GF1).
Olympus & Panasonic are both 4/3's while Pentax & Canon are APSC's.
With all these, i'll choose my Petax K20 over my Canon 40D handsdown (but not over my Oly E30)... Tough and rugged, not to mention fully weather-sealed. It's more weather-sealed and lighter than the 40D.
The only reason i chose my Oly over this is because my Oly is far more lighter than all these and i can use the Leica lens of my Pana GF1 with my Oly...
But Pentax..
"Takes a beating, but keeps on clicking..."