Yahoo! Mail: Simplicity Holds Up Over Time
http://www.boxesandarrows.com/archives/yahoo_mail_simplicity_holds_up_over_time.php

Garrett, Jesse James
Boxes and Arrows
2002

Abstract:

In many respects, email is the ideal web application: it's an application that people often need access to when they’re away from their 'home' environment, and the core user tasks (reading and writing) are easily accommodated with standard HTML interface elements.