My own Twitter bothas been scouring Twitter for the past five years, accumulating over 140,000 tweets containing external links, and today has over 370 users. It is based on faceted classification, using external links for constraint. Automatically selected tweets are not re-posted verbatim, but are normalized (to one degree or another), allowing for de-duplication.
See also my Quora answers to:
(Visited 7 times, 1 visits today)