Yes, they do collect dust like nobody's business. The fan vaccumes it in and it just collects. particularly in my machine which runs pretty much 24/7/365.. Usually I open it up and blast out the dust with compressed air or a vacume. if its really bad I'll pull some of the cards and blast out any dust with compressed air. A typical indication that it's getting very dusty is when even in cool weather the fans run at high speed. A sign that things are getting clogged with dust.

