I've seen far worse in the years I worked at a mom-n-pop computer shop. A quarter-inch of sawdust lining a computer case only begins to cover it. The worst thing a computer can experience is a chain-smoker; those microscopic particles of tar are sticky, and dust clumps to them, creating globs of sticky dark-brown dust. One-time, a guy brought in a machine for his grandson, and we found out there must be more than just cigarette-smoking going on in that house; the case was FILLED with this tacky crap, and when I opened it, I got a headache just inhaling the stale fumes.
Dead mice or spiders were an occasional happening, and once, a rather large live spider.
Intel Q9450 @3.2GHz, Gigabyte GA EP45-UD3P, 4 x 2GB G.Skill @4-4-4-12
Antec P160SW case (modded), Xigmatek 750w PSU
3x 500GB (RAID-5), , OptiArc 7200S, ASUS E818A3T
Creative X-Fi XtremeGamer, Hauppauge HVR-1800, Radeon 4890