I'm obliged to reader H. M. for forwarding me the link to these articles.
The Register, a UK paper, published a picture of a particularly dirty personal computer (below), and invited readers to send in photographs of similarly polluted PC's.
Readers in tech support hastened to send in images of nightmares they'd experienced. Here are a few of them.
There are many more at the link. It's worth checking them out - and then checking your own computer, to make sure it doesn't look like any of them! How some of those computers kept working, I just don't know . . . it offends the former System Engineer in me!