Why not add pleasurability testing into our usability tests?

I just finished reading Aarron Walter’s book entitled Designing for Emotion.  Aarron’s the lead user experience designer for MailChimp.  The book, published by A Book Apart, is a fast and easy read giving tons of examples of websites such as Photojojo, Wufoo and Twitter actually designing for humans.  He remaps Maslow’s Hierarchy to include web user’s needs such as functional, reliable, usable and pleasurable.

One of the tools of a user researcher is usability testing, in which we give a user a task and then observe them as they use the product or service to complete that task.  Essentially, we’re testing how usable the service is, but Aarron challenges us to go farther.  From here on out, whenever you do a usability test, add a few questions to test the pleasurability.  I’m not sure what the metrics for success are for a pleasurability test – I think it depends on the product or service – but we can start with the number of smiles the user makes while completing their task and the number of times we hear “cool – I like that” and “oh that’s awesome”.