The details of what the functionality might be for an individual project may be different now than they were in 2005 due to new developments etc but I would’ve thought the actual concept of what constitutes functionality wouldn’t be any different than what’s outlined in that article.
I read the article and he’s quite right. Basically, with the excuse of functionality, he’s giving you the rules that will drive any site to success: think about your target public, do what they want you to do (and what thye expect from you) and they way they want you to do it, and the faster, the better!
Yes that article is still valid. Functionality is part of the design on any site, a lot of it is about common sense and making it as easy as possible for users to use the site.
Things like consistent navigation, fast loading pages, and a good clear and consise way of presenting the content spring to mind.