[citation][nom]jtt283[/nom]PCs around which people have smoked tend to get filthy very quickly. My wife and I do not allow smoking in our house, although more for our sake and that of our cats than because of the computers. I try to clean my PCs out about every six months or so. Thankfully our cats don't seem to shed very much, but the PCs do get dust and lint in them.[/citation]
Bird dander, especially from Cockatoos, is an issue. It isn't unpleasant stuff - just a white powder - but it gets everywhere. By the way, if you EVER think about getting a bird, do your homework. That white powder is just the beginning. They are very difficult, expensive pets, and require the patience of a saint.