To Tell it or to Sell It

I have tried to be kind and indicate when my opponent's clock is running but after an incidence or two, it's just a burden to me that the opponent isn't doing his job, so I mind my own business at that point.

Maybe if he finds himself fouled up due to this he will pay more attention and take care of his own business.

I wait 2^n seconds before telling them on the nth incident. The exception is when they've made a blunder, in which case I tell them immediately.

I tell them only once, after that they're on their own.

What i would do is to take special note of the time control. I then wait that amount of time before telling them that they lost.

I usually will remind them, though I won't necessarily do it through the whole game. The closer I get to the time control (when I'm running low anyway), the less likely I am to even pay attention to if they hit the clock or not.

Usually, after the first few times they start remembering.

I almost always used to tell them. On the rare occasions when I didn't (usually because they were incredibly irritating and had pissed me off earlier ) I would still take the normal time to think - basically, I wouldn't let the time run down if I already knew what I was going to do.

I think the issue boils down to an etiquette thing. Unless your opponent has already been rude or unsportsman-like to you, you shouldn't take advantage of something that lies outside of the intention of the rules (i.e., someone's time is not meant to run down when it is not their turn). Whenever someone hasn't told me and pretended like they were thinking, it's always rubbed off on me in a really negative way.

That being said, if someone forgets over and over again after you remind them it's not your job to baby them either...

I once reminded my opponent that he hadn't pressed the clock... and he called over the tournament director and complained that I was trying to distract him by speaking to him at the board.

you can pretend to think for hours, until his time runs out

I used to point to the clock when my opponent didn't press his after his move but I don't anymore.  I take whatever time I need to make my move, look at the clock, then not press it.  They usually take the hint.

Well, personally I would tell them...

I point at the clock (not if is a blitz match :D) 

It has happened to me sometimes that I don't realize my opponent did not hit their clock and I move anyways. In which case should I just tell my opponent that their clock is still running and just play on, or is there some process like calling over a tournament director and subtracting x seconds off somebody's clock? I assume it would work like if I were to touch and move a piece during my opponent's turn?

And thank you all for your thoughts. I think I will go with most of the suggestions and let my opponent know the first time or so from now on.

Well, all of it depends on the time control or whether you are winning.

Once, my opponent blundered a rook and forgot to press the clock's button, and the game was 90|30, so naturally I told him. Why simply wait when you are winning?

Instead, if it is a very complicated and unclear situation, you may not want to remind him. And when you have decided your move, re-check, and check the good responses he can give. Then, you could remind him to move when he has less than 5 minutes left. :P

Classy guy.

Once I played a game in a tournament, I was in a winning position and I was moving extremely fast, my opponent forgot to press his clock but I didn't notice it and I quickly moved (again), but my hand reached out too far and pressed his side instead, so I had to press my side again. I was scolded by a coach for pressing my opponent's clock :(.

At least I still won :)

I really hope you won that game.