Tron and WarGames brought "hacking" in the computer sense to the forefront, referring to gaining unauthorized access to computer systems. It's not quite clear how it went from being paid more than you're worth to unauthorized entry of a skilled nature, though I suppose "hacking" may go back to the physical act of hacking at a lock or a door through persistence. Instead of pursuing a goal without the correct tools, now hacking implies pursuing a goal without the correct tools because no such tools exist; it now involves its own skill.
The scope of the term has expanded from unauthorized access to a system to unauthorized modifications to a system. I think that expansion is fair. Moving from unauthorized modifications to a system to making a new system or authorized modifications is where I think many of us draw the line.
If you have a neat idea but the source code and development environment are designed to help you implement that idea, it's not hacking. If your idea requires changing things that somebody's lawyer thinks ought not be changed, then there's a case to call that hacking.
Dunno about its overuse in HN (haven't seen any examples) but the mainstream media and a few overly ambitious coders (and more so the noncoder people who hire them) are definitely misusing the term. Words like "jealous" and "decimate" are also commonly misused but nobody notices.
Now the term "hacking" has been stolen and misused to the point where it has become a synonymous for developer. I suppose no one these days wants to call themselves a programmer or developer as it is a dirty word. Hacker is much cooler.
Some people used a lot more time/resources/motivation than others and they want some kind of title that sets them apart from the rest... I think hacker is the wrong title for them.
A true perpetual motion machine....
For me, if you can use the terminal freely and build something functional REAL quickly by tweaking frameworks/apis, then you are at the starting point of a "hacker".
I think if you have high Karma on HN, you probably care enough about the topics here to be a true Hacker.