dust buildup in/around the drives can be avoided if you modify your case so that the negative pressure causes air to be taken in via a much less restrictive opening. take the bqe for example, i've cut out the front grill and enlarged the bottom opening of the front bezel so that air goes in extremely easily now. also i taped up all the other holes on the front steel face thing.
and... no dust. anywhere. not even on the fan blades.
actually there is a fair amount of dust on the dust filter but that's what tha'ts there for, eh?
This is my exact approach too. I have very, very little problem with dust in the drives of any systems I set up this way. The dust filter gets pretty dusty and gets cleaned every month or so.
In the days before SLK3700's my standard cases were Antec SX10x0 and SX6xx cases that were set up to run positive pressure because it seemed
logical that it should work better than negative pressure from a "dust intake" point of view.
The trouble was, no matter how I tried to configure them, I'd always get dust in the case, and to a lesser extent, the optical drives too. This was the time that I started taping up all the extraneous holes in my case. I was trying to increase the pressure inside the case and force more of the air out through the optical drives. This seemed to make absolutely no difference to the amount of dust that would collect inside the optical drives. I'd still also have a slight dust buildup inbetween the fins of the heatsink, and on tops of the vidcard and PCI cards, as well as dust laying in the bottom of the case. All this on positive pressured, air filter-equipped cases.
About 2 years ago I started getting interested in quiet computers and started thinking about how to reduce noise. The most obvious and easy thing to was to start getting rid of fans and undervolting the fans that were remaining. I started changing my configurations from positive pressure with front fans to negative/neutral pressure with very low flow (or sometimes no) front fans and one or 2 undervolted L1As as exhaust fans on the back of the case. This certainly helped reduce the noise levels quite a bit and after running in this sort of configuration for a while I noticed that there didn't seem to be any
extra dust buildup in the case or the optical drives.
My current type of case setup is a very low flow exhaust fan, a very, very low flow (or no) front fan, taping up all extraneous holes in the case and a dust filter on the intake grill. This slight negative pressure is generally the coolest (temperature-wise) setup to run on most systems that I've played with and I see no particularly bad dust buildup either, certainly no worse
dust buildup than on any of my older "positive-pressure" setups.
In my mind, the "positve pressure = less dust" theory is a myth BUSTED!!
(as they say on TV).