Jakob Nielsen defines the phaenomenon linkrot, and encourages site owners to fight it by reducing outbound linkrot and securing stability of incoming links.
Alertbox article from Jakob Nielsen, explaining how many blogs are too internally focused and make it hard for new readers to understand the site and trust the author.
Usability expert Jakob Nielsen's take on Online Communities: "The Web is not a community: a huge impersonal city is a better metaphor. User-contributed content can be valuable (if edited), but chat rooms should be avoided because of participation ineq...