We're moving into what I call the era of the "Casual Web" (and casual content creation). This is much bigger than the hobbyist web or the professional web. Why? Because people have lives. And now, people with lives also have broadband. If you want to hit the really big home runs, create services that fit in with - and, indeed, help - people's everyday lives without requiring lots of commitment or identity change. Flickr enables personal publishing among millions of folks who would never consider themselves personal publishers - they're just sharing pictures with friends and family, a casual activity. Casual games are huge. Skype enables casual conversations.
From Ev Williams' excellent Ten Rules for Web Startups