Infrared thermometers work very well when measuring the temperature of hot oil.
For deep frying it's not a big deal, as standard probe thermometers work fine.
But for shallow frying or sauteeing, the IR thermometer does an excellent job at providing the temperature of the oil.
(Note that IR thermometers are not accurate when measuring the temperature of a dry steel pan, as the shininess makes the pan look much cooler than it is.
IR thermometers work fine on dry cast iron pans, though!)
IR thermometers work rather poorly when measuring the temperature of hot water, however!
Rather than measuring the temperature of the water surface, which is usually similar to the mass of the water due to convection, it measures the average temperature of the water vapor coming off the surface!
In my experience, boiling water measures about 200 F with an IR thermometer.
cooking.stackexchange.com/users/45/Harlan
One thing I've found surprisingly useful is how accurate it is measuring the temperature of microwaved liquids.
This can be handy when bringing milk or water to 100 degrees when making yeast breads.
The convection of the liquid when heated by microwave means the surface temperature is within a degree or two of the center of the liquid, at least in my experience.
For hotter liquids, where the water vapor is cooler than the liquid, it may better to measure the side of the pan below the water level.
cooking.stackexchange.com/users/45/Harlan
They can also be used to get a quick reading on the grate temperature of a grill.
Probably not as accurate as a grate mounted thermometer (sometimes seen inside a smoker) though.
cooking.stackexchange.com/users/258/TonyB
Great for making yogurt & checking temp of boiling milk @ 185f + cooling to 115f.
Its critical to get the correct temp or you will kill the culture used to make the yogurt.
Works like a charm!
cooking.stackexchange.com/users/14091/Dave778
I bought one to measure the temperature of a firewood oven.
Immediately I noticed it was useless.
In order to bake on those ovens, you must have enough temperature in the bricks, not just it their surface.
Using the terminology: They have to be soaked.
Luckly I had built the oven with plenty of sensors between them.
But there is one dish which needs a lot of temperature in the surface of the oven: pizza.
Unluckly my I.R. thermometer could only read up to 325ºC (or so) (600 ºF).
That wasn't enough for pizza.
So I bought a new "expensive" I.R. thermometer that reads up to 900ºC (1650 ºF).
Now I know greater pizzas are made between 400ºC and 450ºC. (750~850 ºF))
cooking.stackexchange.com/users/14096/J.A.I.L.
You can't measure the inside temperature.
You will just get the superficial temperature which is usually almost useless.
You need a thermometer that can be inserted in the food (for example a meat thermometer) and then you will be able to do exciting things, for example the perfect temperature for frying oil (just under the smoke point) or the steak grade (raw, medium, well done).
cooking.stackexchange.com/users/16/Wizard79
The best use, imho, would be to make sure your oven was hitting the correct temperature.
Other than that, I can't think of anything cooking related.
cooking.stackexchange.com/users/218/Satanicpuppy
As a BBQ master, I use IR thermometers to measure grills for correct temp or find hot/cold spots.
However you cannot just read the grill straight down as the IR will read the flame or flame tamers down below.
However if you cast your eye at an angle to the grill until you cannot see below and take a reading at that angle, It will read the surface accurately.
I also use the IR gun for pressure frying where the oil temp is critical before sealing.(Dont try pressure frying unless you know what you are doing)
cooking.stackexchange.com/users/22557/Smokey
Infrared thermometers have plummeted in price in recent years, and are now inexpensive gadgets for the home cook, not to mention the pros.  What are the primary uses of an infrared thermometer in the kitchen?
What can you do with an infrared thermometer?
cooking.stackexchange.com
<temperature><equipment><heat>
cooking.stackexchange.com/questions/1093
cooking.stackexchange.com/users/45/Harlan
IR thermometers are useful for measuring the temperature of grills, hot oil or liquids other than water. IR thermometers are useful for measuring hot oil and milk but less good for boiling water. They can be used for a BBQ grill.
IR thermometers can be used for measuring liquids like hot oil or milk and to test the temperature of a BBQ grill. IR thermometers are not very useful for hot water.