My 5D viewfinder is among the brightest I have used. If I mount a F2.8 lens on my EOS 5D, Elan 7, Nikon FM3A and EOS 3, the 5D whips them all and good. Often folks speak fondly of their ultra bright F, FA or FM series body but forget their memories are based on a fast prime, e.g., 50 1.4, and not a slow zoom, e.g., 24-105 4L. Mount a slow zoom on that old FM, FA or F2 and it will look even darker. The 5D has a dad burn fine viewfinder. Top notch.
As for the exposure data backlight in the VF, I agree, it's a little on the dim side. Both my 10D and Elan 7 are a notch brighter. However I can read it without problems in the bright sunlight of Hawaii, so no biggie (of course no problem in dim light). Plus, I'm normally too busy shooting to worry about the the display. Sheesh, I just set it so no problem remembering my settings. Of course I don't smoke mary jane so the short term is still happenin'
However the rear TFT is too dim to use in bright light. Shooting on white sand beaches I can't even read the histogram. In fairness, most TFT are useless in bright sunlight but the 5D goes one better and is totally and completely useless. I normally chimp after the shoot so no biggie again, but if you grew up a digicam you'll feel naked.
Incidentally, no VF or CMOS dust problems for me. And my 5D is exactly 1 year old this month.