I don't know the Reddit history that well, but as I read recently in a PG essay, it was originally slated to be a food ordering application on your phone.
I do not know when they pivoted, or when their idea to pivot came, but I _suspect_ that their pivot was at least partly inspired by Digg's early release.
metafilter predates both Digg and reddit by 5 years, and was enjoyable for quite a while longer than either of them. I don't think it's fair to credit either of those sites with social bookmarking.
