Tom Negrino was looking for a particular pair of shoes, and called Zappos. They didn't have that model, so the customer service agent actually sent Tom to a competitor's website.
And stayed on the phone to help him make the purchase.
Now, it's entirely likely that Tom would have been happy if the agent had simply offered him a comparable pair of shoes, and Zappos would have made a sale.
Instead, they went above and beyond to help him find exactly what he was looking for, and gave up the near-term revenue. You can bet, however, that the next time Tom needs shoes, he'll go to Zappos first. And probably the time after that, and the time after that....
Plus you can't beat the free publicity of getting written up here on The Customer Service Survey.