Design guru Jakob Nielsen writes about the Top Ten Web Design Mistakes of 2003. He makes several salient points (and a couple pretty minor ones--'overly detailed ALT text'?), among which my favourite is:
Undated Content Without dates on articles, press releases, and other content, users have no idea whether the information is current or obsolete. It's great to keep content in archives. The Alertbox, for example, gets 80% of its readership for old columns, which readers continue to find useful. But some facts and recommendations are strongly date-dependent, such as when I recommend using a certain version of a software package for another two years. Obviously, I mean two years from the day the article was written; if readers can't see the date, they won't know how to follow the recommendation.