I use it in my 66 GTO. 400 cubic inches at about 12.5:1 compression, it will hardly run on regular. I spent quite a bit of money on the engine so it will run on unleaded, I’m not going to risk it just to save a few bucks.
For the extra dollar a fill I put it in my motorcycles. For the 2004 pickup, I’ll use anything.
As it was explained to me, the only cars that gain any benefit from premium are those whose engines were designed to use it. There’s something about there being more solids in premium so it burns slower/more completely and doesn’t cause some sort of engine fireball.
Thanks, everyone, for your very interesting responses. I am not a driver, and my wife’s car takes regular unleaded. I guess I haven’t known anyone with a high-performance car that required the highest octane gas. I don’t envy what you have to pay for it, but the way things are going, the rest of us may be paying that much for regular soon.
I think this is the GQ thread lieu was referring to.
My Lexus requires premium, and I haven’t withheld it. It’s not quite 10 years old, has 275,000 miles, and has never needed any engine repair at all.
Sometimes following instructions is the right thing to do.
Hmmm, looks like a thread full of potential runners on a 1/4 mile. E-mail me for info and risking pink slips. The answer, adjusted for preferance is, if your engine requires it, use it, if not no. Your milage may or may not vary.
My BMW Z3 gets only the good stuff. Really, the difference in price is just a few bucks - it’s not like normal unleaded is $1 and premium is $2.50. I don’t see any reason not to use it, since it’s recommended for my car.
I have a 2003 Ford Focus. Not a fancy car by any means, but I have never put anything in it but the very best gas. Lately it’s been costing me about $32.00 to fill up my tank. That’s a lot of money, for me.
My car is a 1995 Ford Escort, many dings, filthy dirty, makes loads of funny noises, only my second car, but I totally think my car is great, because it runs and it’s my buddy! My car gets regular gas always, because it seems to tolerate it well, and most importantly, regular gas is the cheapest.
The cheap stuff for my truck !
When you have a 40 gallon tank, and it is $2.25+ a gallon = $90 a fill up!
w00t!
The Nissan 3.5 L V-6, in whatever model it’s in recommends it. There’s some noticeable benefit performance and mileage wise, but the bigger difference as others have pointed out is long term. I use it. I don’t drive enough that the extra $3-$4 a tank is a hardship.
My mother-in-law drives a Cadillac and only uses premium. Dave and I both use regular in our vehicles.
Because they cannot afford to drive? 
I put whatever is cheapest into my Jeep’s tank. Although there is one station locally that has the grades reversed (premium button on the left) which tricks many people (myself included) into buying the good stuff. My Jeep runs no better to my humble senses with the good stuff.
I buy the premium stuff for my Mazda 323 Astina SP20. It’s what’s recommended by the manufacturer, so that’s what I buy.
Still, it doesn’t stop me from balking at the fuel prices. It’s a 10c price hike over regular fuel (ie a 10% increase). When prices go above $1.05 a litre, I buy just enough fuel to see me through for a couple days. In practice, this means I spend $20 every third day.
The irony is that I got rid of my 4L 6 cylinder Ford Falcon wagon because it was costing me a truckload in fuel. Now, my Mazda uses far less fuel… but the fuel costs more. So I’m paying the same for fuel now as I was before! GAH!
Max 
Delay is not a very good word to use here IMHO. Inside the cylinder the gas and air are compressed to almost the self ignition point (gasses heat up when they are compressed) The spark ignites the mixture, and it burns. As far as I know both premium and regular burn at about the same rate. As the mixture burns, the pressure and temp in the cylinder rise. With a low octane fuel, this increase in temp can cause the fuel to explode, rather than burn. Higher octane fuel is more resistant to explosion, and the burn continues normally. When the fuel explodes rather than burning, you get two flame fronts in the cylinder, and a noise is produced when these two colide (ping!)
Now a modern engine control system detects ping, and since ping increases tailpipe emissions, the ECM (Engine Control Module) takes steps to prevent it. one way to lower the chance of pinging is to lower the peak pressure in the cylinder. This is done by delaying or retarding the spark to the cylinder. Some of the engine management systems I am familar with can retard the spark up to 17 degrees off of the mapped timing. This is a bunch and will have a for sure effect on performance. The reason the ECM does this retard is that ping is a type of missfire. Missfire both increases emissions, and well as can destroy a cat converter in very short order. In severe cases missfire can damage the engine.
So saying that premium “delays” the combustion is wrong. The combustion event is determined by the ECM. If the fuel does not have a high enough octane rating, this event can and will be delayed. Retarding the timing can lead to a reduction of power, to prevent an increase tail pipe emissions.
Me, I run what the car maker suggests.