Think about this in the context of a company. You may want to allow people to quickly search for bookmarks flagged by others at the company.
For example: ‘hr vacation policy’ or ‘project foo’
You've hit the nail on the head :)
I'm not using social bookmarking either, but I can see the appeal of being able to discover quality resources easily (when following reputable people). That's basically what "awesome lists" on GitHub are for.
del.icio.us was big back in the day, before Yahoo ruined it, so I guess some people want it? Although, to be fair, that was before recent privacy letdowns.