> You can upvote it to bookmark it
...
> You can upvote it to say "Yes, I would like to see more of this on HN."
I'd do a lot more of the latter if not for the former. Because HN uses the same mechanism for both I tend to avoid up-voting stories unless they are stories I want to bookmark for later reference. If they are just interesting but not something I think I'll need to refer to later I avoid up-voting so as to not clutter up my bookmarks.
I wish HN separated up-voting from bookmarking, like Reddit does.