Digg's main problem is it left the technology niche and became mainstream. The same thing has happened with lots of forums I used to frequent - for example, one

Digg's main problem is it left the technology niche and became mainstream. The same thing has happened with lots of forums I used to frequent - for example, one broadened their focus from a highly technical media broadcasting community, to a TV entertainment and gossip portal. The traffic increased dramatically, yet the quality of the posts dropped. Hacker News will be fine so long as they keep things controlled and avoid the pull of the mainstream.