It is a classic example, used many times to explain data mining.

However, it is not true:

http://www.theregister.co.uk/2006/08/15/beer_diapers/

Seriously, have you ever been in a supermarket where beer and diapers are next to each other? 😀

Better examples I've found in every day life:

* supermarkets use data mining to see if a promotion on a product was succesfull and to see if the products in the intermediate area of said product sold less or more.

* supermarkets also use data mining to send you "personalized" coupons

* Amazon uses data mining to suggest you books that might interest you. (this is correlation. Amazon checks the books you've bought or looked at, and uses these to find books that are highly correlated with those. As more and more people come at the Amazon site, the correlation algorithm gets more and more precise.)

* analysis of the customer base to find a certain demographic that might find a certain brochure interesting