Hacker News, Reddit, and bookmarks in your browser don't do the same thing. The former two because links you submit to them are not considered "yours" in the same way del.icio.us and Pinboard, and browser bookmarks because they are not social in the same way.
I guess Twitter does the same thing for a lot of people but it isn't as focused and it doesn't feel the same to me.
Does anyone else have any thoughts? Is social bookmarking forever relegated to a niche market or...?