I think the build of my 40D is so much better than my MarkII..

Used 40D for abt 2 years and there is no single bit of dust on my viewfinder while for MarkII, used less than a year and i have at least 4 spots of dust TRAPPED on my viewfinder. 

Fortunate thing is that it doesn't affect the images... but i just find it an eyesore.. Last weekend i even spotted a ant like insect crawling across my viewfinder!!!