I believe an important aspect of Agile is not only releasing what is functionaly requested by the user base and generating revenue for features/product that people want to buy vs. features no longer wanted, but usability has to come into play as well. If you deliver working software without the desired usability, you still haven’t succeeded.
I would also recommend reading Damon Poole’s blog from Accurev. Some very insightful and regular posts that we find valuable.