I was really chilled by this article on how easy it is to crack even seemingly-unguessable wi-fi passwords. I haven't kept up with the state of the art, and didn't realize how convenient the password cracking tools have become, nor did I know about the "deauth" trick the author describes.
The bottom line is, your basic Internet security hygiene now needs to include using uncrackable wi-fi passwords, particularly if you live or work in a wi-fi dense area that presents a "target-rich" environment to an attacker (such as the one where the author's office is located).
But what are you supposed to do, tell every house or business guest who wants to get on your wi-fi that the password is "Heyw00Dj@buZZoffe!!!69ass353q1"? That's lame. Instead I recommend choosing a random, distinctive passphrase of easy-to-spell unrelated words, separated by spaces.
For a business, I would also recommend changing the password on a regular basis. Many routers also have a "guest network" function that provides an isolated network to guests. That way you don't have to give guests access to your internal network in order for them to hop on the Internet.