I don't think it died as much as it captured the early adopters, which by definition represent a limited market. In my case, it's a great tool for archiving research. I'd describe social bookmarking as aspirational in the sense that a lot of what I bookmark is for future projects around current and latent interests, which I know some day that I'll return to. That's maybe a use case for the creative class, and not something as passive as reddit browsing.
Take Shirky's power law distribution ideas around content on the internet. A small percentage produce, another percentage participate and by far the largest percentage consume. Social bookmarking is a kind of curation that is in between the producing/participating levels. Much of the social aspect has been gutted by Twitter (which wins in terms of sharing, but drops the folksonomy and organization and production of a research repository), but what Twitter drops affects almost no one outside the 1-5% who are in that produce/participate space.
Take Shirky's power law distribution ideas around content on the internet. A small percentage produce, another percentage participate and by far the largest percentage consume. Social bookmarking is a kind of curation that is in between the producing/participating levels. Much of the social aspect has been gutted by Twitter (which wins in terms of sharing, but drops the folksonomy and organization and production of a research repository), but what Twitter drops affects almost no one outside the 1-5% who are in that produce/participate space.