I'm all for describing things in terms that most people can grasp. For example, in my forthcoming book I make the point that if a transistor (the fundamental building block of computer processor chips) were the size of a (UK) postage stamp, then ten years ago, the average chip would be the size of Snowdonia National Park in Wales. With the advances in chip miniaturisation that we have seen in the last decade, the same chip in 2005 would be the size of Iceland.
Readers of the New Scientist will be aware of an ongoing discussion of the use of Wales as a metric (hence my tongue-in-cheek reference in the book). However, I'd like to draw your attention to a far more insidious comparator: the human hair.
There seems to be an unwritten rule of science journalism: any article dealing with micro- or nano-scale technology must, at some point, compare the scientific breakthrough in question with a human hair. Some recent examples are here, here, here, and hair.
I'm not questioning the quality of the science, or even that of the writing, I'm just sick of seeing constant references to hair in popular science articles (maybe because I'm losing mine!)