I still maintain that Google killing Reader to make room for Buzz and Google+ is what really killed the best of the old web. Even though RSS readers only ever had purchase with a minority of internet users, they clicked with the most "influencery" people who would go on to share what they read. IMO, that sort of serendipity and discovery is what Facebook and other service try to replicate now through their algorithmic curation. They're trying to mimic the natural virality that content used to take, but it's forced and, consequently, lacks the same kind of whimsy since too many people are too good at gaming it out. It's all structured to try to sell us something.

RSS readers still exist, but Reader's ubiquity and its social features are really what seemed to tie the web together into a cultural force. At least among my circle of people.