It's relatively new. Before we used upvotes. Actually I still don't use it and keep using upvotes to favourite stories. I'm sorry for that and even worse: sometimes I upvote a story without following the link, just using the upvote as a "read later" bookmark because I found the title intriguing. Not so bad is when I upvote because there's a very interesting comment, even though the article itself is crappy.

Time ago someone posted a script that collects upvoted stories, but I can't find it now, it's in one of those upvoted stories O:) I guess I could make a conversion... but there are probably more than a thousand upvoted stories, I don't know.