What are people's opinions on fuel additives? Stuff like octane boosters and engine cleaners?

I recently put in a bottle of this chevron techron stuff.. (with a new tank 92 octane of course) It says that it boosts octane and cleans out the fuel and combustion system.

I have read that the higher the octane, the better, cooler, and quieter your engine will run.

For some reason my motor sounds LOUDER? I did get a new air filter recently.. maybe that has something to do with it? I do notice a slight increase in "juice" but not a lot.

Also, I am noticing a very, VERY slight hesitation when accelerating. It seems to do this in all gears, at about 2500k rpm. It also seems to get better when the car gets warm, and eventually go away. I didn't always do this (but it is getting colder at night).

What are the typical things to check first? Fuel filter? Pump? I don't even know where these things are located, I am total newb with cars.

Thanks.

Oh yeah, ’99 Accord EX coupe 5spd, stock