Would it do the same thing if your microwave had a turntable ?

The reason water superheats has little to do with the microwave oven you have, and more the container it is boiled it.
A ceramic cup, or pyrex glass, when new are near perfectly smooth down to the atomic level. Most water is to all extents "pure", unless you live a a very hard (chalk flakes in the water hard) water area. As a microwave excites the water in the cup as a whole relatively evenly, not like a pan where only the bottom of the pan conducts heat to the water, causing water to "convect" (hot water rising as it becomes less dense, making the water circulate from to top to bottom), the water can receive more energy than it needs to boil into a gas.
This is because for a bubble to form it needs a point to concentrate on. This can be a pressure wave through the liquid, like that caused when water circulates. You can test this yourself, get 2 bottles of larger and a friend. After opening your friend's larger, tap the lip of the open bottle downwards and watch as the gas in the larger is released by the soundwave travelling through the glass into the larger, and he calls you a dick for covering him in beer.
Another way gas bubbles form is on scratches and imperfections in the container walls. This is why bubbles form on the inside of open lemonade bottles, a scratch on the bottle wall allows CO2 molecules to condense (long boring explanation why, basically static electricity on a very small scale). Once a bubble forms it causes pressure changes in the surrounding solvent which then allows other bubbles to form.
In a new cup there are no microscopic scratches yet, and as the water is heated from the centre outwards, no convection currents form. So the still water can superheat. Which then explosively boils the moment you move the cup/put a spoon/milk into it.
If you have a new powerful microwave and a new cup,put a wooden chopstick in it or stir it first before heating up your tea or coffee.

"Superheated" water has been an issue in Australia for over 10 years--particularly in high-power ovens (> 2400W) where the water can exceed boiling, but the glass is still cool to the touch.

Pyrex and glass are the worst offenders. As cited elsewhere porous materials are safer, and water purity plays a major role.

Drop a sugar cube in it....JUST LIKE MYTHBUSTERS! (they used distilled water btw)

The water in question is likely distilled water (or water with very very little to no impurities in it) Water boils due to the impurities in it (part of the reason to add salt to a pot of water you want to boil, the other is to raise the boiling point so when you add food it doesn't take as long to get the water and food simmering or boiling again) So it you take distilled water, raise its temperture to the boiling level and then add an impurity( salt, suger, whatever is naturally on the spoon or whatever he added to the bottom of the spoon) you will get a flash boiling which will tend to cause very hot water to splash and shoot out of the container it was heated in.

I fail to see what conditions you use to cause the water to boil. I'm sure we all know the facts about this, but if you could add them to the Instructable? Just for the record, every day I heat up my large coffee mug of water to make some 'Chai Tea'. The microwave has always been set to three minutes and thirty seconds. (I like the drink extra hot :) ) Not once have I had this issue 'pop up'. :P

very cool.

He isn't even wearing gloves! Jeez he's just asking for it!

No no no... The minerals in tap water cause the water to boil (like the fork). Only pure water has a chance of exploding like this.

tap water CAN do this.... part of the "trick" is using the glass glasses... 99.8% of ceramic mugs have tiny cracks in the glaze, in the bottom of the mugs. these cracks for a point where bubbles form... sort of like a seed crystal. and once the bubbles start, the risk of exploding water goes away. The danger is in the "hot enough to boil" water, that has not had a chance to divulge it's entrapped air. Once disturbed.. the water, which is at that point supersaturated with gas, unleashes a majority of the gas all at once, hence the explosion. good information to know, but not really sure it qualifies as an "instructable"

actually a cup of milk coffee done this to me once O.o i heated it in the microwave 8after about 3 other cups for others) and when u put in the spoon to stir it out jumped the drink :D there was only a little bit left in the bottom :( it only happened to mine tho :S