As nifty as this is, I can't help but think that I'd be a lot less excited about the green Jell-o in this video [1] after blasting it with salt.
Also, the FAQ [2] doesn't address whether or not it works against horse flies [3]. Those fellows don't always go down when you swat them against your skin. If you've been fortunate enough to never have been bitten by one, I can assure you that it's not for lack of effort. A horse fly bite will get your attention in a hurry.
Horse flies were the number one cause of running around like crazy on the pool deck and then jumping into the pool and holding your breath when I was a kid.
If you're using firefox and can install extensions, I recommend noscript [1]. Admittedly, it'll take some time to whitelist all the stuff you actually want to work, but it does cut down on silly stuff like the fly (which for me remains parked in the upper left-hand corner). There's apparently a Chrome extension called ScriptSafe if that's your browser of choice.
And now you have me wondering if your comment gets a new id when you update it. If so, convincing people to execute random javascript code could be a good way to build karma. Let's find out :-)
$('#up_5210561').click()
EDIT: Comment id's remain the same when you update them. Now for the social engineering aspect...
Ideally one would embed a webpage with a hidden image that loaded the upvote URL for a particular post of yours. Every logged in user would unknowingly upvote that post ID. Thankfully HN is built with form keys, so that particular CSRF attack won't work.
Social engineering would be more difficult, I seem to remember that Chrome prevents javascript strings from being pasted into it's URL (you can still type them), in order to prevent attacks just like this. There was a number of attacks on Facebook that involved asking users to copy and paste a dodgy looking javascript string into a Facebook tab in order to "win" something. Of course it just spammed posts and stole session information, but it was still an interesting attack.
Got one of these for my parents for Christmas. Waiting for flies to come out for a true functional test, but the device is solidly built and does a number on a sheet of tinfoil :) a little pricey but a interesting and seemingly well-made gadget.
Also, the FAQ [2] doesn't address whether or not it works against horse flies [3]. Those fellows don't always go down when you swat them against your skin. If you've been fortunate enough to never have been bitten by one, I can assure you that it's not for lack of effort. A horse fly bite will get your attention in a hurry.
[1] http://www.youtube.com/watch?feature=player_embedded&v=i...
[2] http://bugasalt.com/faq/
[3] https://en.wikipedia.org/wiki/Horse_fly