I have already raised this issue, everyone told me it's a normal thing for the 3rd gens. I noticed it more after towing a good-sized load, but WAS into the brakes a lot more than my usual driving. I have about 24K miles or so, just rotated my tires a few days ago, the pads had tons of material/meat to them, so I guess the dust is not a sign of great wear or the need to change them.
Comes off easily at the car wash with plain pressured water. I wash about once a week and have about the same amount of dust each time.
CD