I just reread the HN guidelines (it had been a while), and was surprised that flagging stories is apparently intended to be used more liberally than I had thought. The relevant sentence is:
If you think something is spam or offtopic, flag it by going to its page and clicking on the "flag" link.
I had been considering story flagging to be used for abuses like blatant spam or flaming, but not merely to express one's personal judgement of whether something is on-topic ("anything that gratifies one's intellectual curiosity"). Obviously, different people's intellectual curiosities are satisfied by different things, and I had thought that story upvoting was the means to express that judgement.
I have heard that rumor as well. Interestingly, HN's description of story flagging sounds nearly identical to Reddit's (informal) description of downvoting (presumably referring to both stories and comments):
If you think something contributes to conversation, upvote it. If you think it does not contribute to the subreddit it is posted in or is off-topic in a particular community, downvote it.
Of course, HN doesn't have downvoting for stories (unless that's a feature I have yet to unlock), while reddit has downvoting as well as reporting (with options for spam, vote manipulation, personal information, sexualizing minors, breaking reddit, and other). I had been operating under the assumption that HN flagging was analogous to reddit reporting, but it would appear that HN flagging is intended to be more analogous to reddit downvoting.
If you think something is spam or offtopic, flag it by going to its page and clicking on the "flag" link.
I had been considering story flagging to be used for abuses like blatant spam or flaming, but not merely to express one's personal judgement of whether something is on-topic ("anything that gratifies one's intellectual curiosity"). Obviously, different people's intellectual curiosities are satisfied by different things, and I had thought that story upvoting was the means to express that judgement.