People upvote if they liked the story, and they vote just to share.

Not sure if it's typical but I almost never upvote a story (however I'd happily downvote some of them if I could). Last time I checked it automatically saves it in your favorites. Since I never go back to check a story, no matter how interesting (in which case I'd just hit Google), I find it would be an utter waste. Accumulating stuff I know I will never use like that seems... frightening to me, for some reason.

My usage pattern is almost the exact opposite. If I like a story and find it relevant, I upvote it in part so I can easily reference it later.