If only the hash value is mailed, then the full key can be e-mailed or anonymously posted to a newsgroup that you montitor. If the full key is mailed, you should invest in a scanner and some simple OCR software.
I have been thinking about this. I think that pgp should have a postscript output module, so you can print your public key on the back of business cards and hand them out to people you meet. Or businesses could put it on thier flyers. Or many other uses for times when you don't want to have to have your computer there to exchange keys and you don't want to exchange disks because they're expensive and big and have lots of different incompatible formats (and some people, like me for instance, don't have any disk drives). I think the best font for this would be a font like OCRA, the font used at the bottom of checks. This font allows for very reliable scanning. Does anyone know where I can get a postscript version of this font? If someone can find it, I'll write a program that outputs a public key in that font in the right size for a business card. e