We have two rabbits. They have never been hit.
It would be animal abuse, and anyway it just makes them (rabbits) aggressive in turn. Relaxed rabbits on the other hand are easier to train.
My cat, no.
My Staffies who have since passed on to doggie heaven, no. I have, however, had to resort to Alpha Male tactics when they got into fights with each other. This entailed grabbing them by the scruff of their necks and separating them, followed by a stern finger-wagging-stop-your-shit-I’m-the-Big-Dog-in-this-yard lecture.
Here’s a technique my mother came up with for getting our dog to settle down when she gets riled up and starts barking and jumping everywhere.
Take a rolled up newspaper (no, it’s not what you think!) and then slap it very hard against a hard surface (the wall, a table, etc). It may take a few times, but it gets her attention, and she doesn’t like the noise, and she’ll usually calm down.
I will admit to threatening my cats all the time-my favorite is “I’m gonna cut your tail off and whip your ass with it!”
My kitty gets a sharp tap on the noggin if she’s misbehavin’. Or, she’ll get picked up and dumped in her “room” (actually the laundry where her litter tray, bed and food bowls are) for some “quiet” time. Sometimes I actually think the quiet time is more for me than her but she settles down after that.
Or else she gets the water spray bottle. After a few mountain-climbing expeditions (where she’d climbs the brickwork) she soon learned.
The only other naughty behaviour she regularly does is climbs the front door’s flyscreen door where she makes it to the top left corner. Why she likes this corner is anyone’s guess but she quickly detaches once she gets the water on her.
Fortunately, she bears no grudges after being told off. Five minutes after she’s had a “talkin-to”, she’s back on my lap/stomach/neck demanding to give me kitty kisses whether I like it or not.
Oh yeah, I beat my turtle senseless every day. 
He doesn’t notice it, though, as he’s usually sleeping anyway. Or begging for food.
I have done and will continue to do so when conditions warrent. The last time I hit my cat was when she was jumping up to the lit stove. I hit her in mid air and deflected her so she wouldn’t have landed on the burner.
The time before I was doing some remodeling and my cat (another one) tryed to jump up onto the windowsill, problem was the window was removed. Again in mid jump I hit that cat back onto the floor as opposed to that cat jumping out a 2nd story window.
Hitting a pet can be a very good thing.
I have 2 cats and if they are tearing up furniture or doing something dangerous they get swatted on the backside. Both of them seem to get the point and they even have a vague sense of right and wrong. If I yell at the older one for something the younger one did I get a lecture.
For lesser infractions I thump them on the head like a melon. Seems to work well during nail trimming time. That and the back rub afterwards.
I would never hit my dog because she’s the most timid, submissive dog ever, and a harsh word wounds enough. HOWEVER, when I tried to wrestle one of my cats out of a pit bull mix dog’s mouth, I smashed that thing in the head with a large flashlight for what felt like hours, to no avail. Didn’t even leave a MARK and certainly didn’t faze the dog whatsoever. This, however, was a life or death situation, so it isn’t really the same thing. But it made me wonder how effective hitting a large dog in the head (or anywhere else) could possibly be… unless the dog already has a relationship with you where he wants your approval and actually gives a damn, in which case you really wouldn’t have to hit too hard to get the message across.
As for cats… 3 of my cats were adopted as adults and they have, on occasion, bitten me when they’ve gotten too excited. They get a light tap on the nose, accompanied by a loud “OUCH!” that suffices to get them to lay off. It’s as hard as tapping a human on the shoulder, and it’s a token gesture of irritation. They do much worse to each other when they’re doing their WWF (World Wrestling Feline) play.
To me, hitting your pet or a child MIGHT be required IF someone could get hurt or was being hurt, and concrete, immediate intervention were necessary. In that case, it should be more of a symblic gesture, enough to get the individual in question’s attention, so he realizes the gravity of the situation, then knocks it off. Actually causing pain when using physical discipline on pets or children seems entirely unnecessary to me and I personally wouldn’t do it, or even come close to it.