Jakob Neilsen's latest Alertbox looks at the applicability of user guidelines over time. He argues that they are pretty durable and looks back to 1986 guidelines to make his point.
The following was an interesting comment:
However seductive the present might be, writing for the Web is writing for the ages, not just for the moment. (People who post stream-of-consciousness entries in their weblogs, for example, might want to consider that they're also writing for managers who might hire them in twenty years.)[Durability of Usability Guidelines (Jakob Nielsen's Alertbox)]