It was a joke.
It’s up to Joe to correct the error if he desires. MYOB.
I’ve had an employer overpay me, and I definitely gave the money back. Companies take that sort of thing seriously, IMO.
I didn’t know that and I’m happy to hear it, especially considering your profession! 
In regards to the other, I’ve also been given more money and gave it back. Not because I am such a good, wonderful person, but I know eventually, but before the end of the year, they WILL find their mistake and demand it back. Better to give it back right away.
Yeah, I’m in the same boat with most of the responders – it’s none of my business, and up tp Joe as to how to react.
Now, if I’m Joe, I’d point out the mistake and offer to return the check. I don’t know about the US, but I strongly suspect that here (Israel) the result would be HR giving me something but less than $500 (most likely some kind of gift certificate for a nice breakfast for two at a good restaurant, or a 4-hour spa voucher for two.)
Not likely to have that happen here. There’s a joke buried in here as a result that I’m not brave enough to mine out and refine for public consumption. But it’s in there alright.
Not even I would tell. Not even by inaction am I doing anything wrong, and I don’t see Joe giving up the money actually helping anyone. I probably wouldn’t have thought of telling Joe (as I’d assume he’d notice a $500 bonus), but I might since you guys mention that apparently the company would be likely to actually ask for it back. (I’d be more inclined to think they’d fire the employee who made the mistake.)
Any error is between Joe and the company.
Is this based on a real life situation?
You know, I couldn’t figure this out. So I scrolled up and noticed it was ME who gave you your new username with that typo!
Give the money back. There. That’s what the butchered type should have read. I suspect, since it was glossed over, most figured it out.
I must say, my iPad has the very worst auto-complete dictionary on the planet. Half of the mistakes I make I’m not even aware of. I have to find out if there is a way to Fix the auto-correct choices.
If I was close with Joe, I might say something like “Well, aren’t you the luckiest guy on the face of the earth! A $500 bonus, all because HR screwed up! Too bad you have too much integrity to actually keep it. Oh well, easy come, easy go.”
I’d say it in a light-hearted way. If he keeps it, frankly it doesn’t affect me one iota. If he returns it, good on him.
Not your business.
Either Joe will keep it, or return it. That’s on Joe. Don’t deny him the chance to do the right thing, on his own.
If Joe keeps it, someone in accounting may figure it out. They may choose to cover it up, with nothing more than some chastising. Pointing it out, may change that outcome, in not pleasant ways, you have no way of knowing.
Stay out of it. It’s not your $500. You’re not Joe.
Yeah, this. I voted ‘Good for Joe!’, but if I were Joe, I’d be worried that it’d be remanded right at the worst possible time.
Yeah, just turn it off. At least then you know that any mistakes are your own, and not borrowed. 
and it would still show on his W-2 8 months later.
No.
We’ve already covered that HR HATES employes (i.e. not our for their intrest) but if they screw you over, why wouldn’t you stand up for yourself?
Found 1.
They’re NOT a “busybody”, they’re a person of INTEGRITY with a clear conscious! America could stand to have MORE of them, not fewer!
This happens quite a bit in the military (not rewarding new ideas, HAHAHAHA) when certain extra pay that’s dependent on different situations doesn’t get shut off when it should. They always take the money back and it’s rarely enjoyed by the military member when they do. Usually there’s some cry of, “It’s their mistake, I should get to keep it since it wasn’t MY mistake.” Which is, of course, bullshit.
I wouldn’t tell, I don’t need to; the glitch will fix itself.