Well, of course it's the people. I started online in '94 and it was exclusively the territory of nerds for a long while, even as everyday folks started to use the web and email for basic things. Truly, we should appreciate having places like Hacker News for still giving us a place to post like we always used to...

Plenty of forums still do exist, but I wonder about their future as we age out. Car forums in particular were absolute godsends for amateur mechanics - not just to look up info but to ask a self-selected group of interested folks who were happy to help for free out of a sense of community for fellow fans of their brand.