Teamleader.. Think of it this way. Microwaves consume 1000-1500 or so watts of power. They put out most of that as energy in the microwave range. Mind you puting anything besides food in a microwave can cause damage to the microwave itself, metal especially can cause feedback in the magnetron and bad things will happen. Mad scientist stuff is fun, but you have to be very conscious of saftey. To do otherwise can easily kill you or someone else and cause property damage.
All that being said CD's are particularly interesting to watch in a microwave. Also if you put a lit match in a microwave the extra energy from the microwave will actually create plasma balls that float around in side the oven. Yes, I said it, home made plasma. This is VERY dangerous to the microwave though. Search around on google and youtube, you'd be surprised what you can do with a microwave.
For basic saftey tips I would say, make sure you have a fire extinguisher nearby (CO2 ones work well) Make sure there is several feet of space around the microwave and aside from that this is best done outside or in a large basement where there is nothing flamable nearby and PLENTY of room/air. Make sure the microwave is fused right at the outlet (don't rely on the house breaker) And unless you know exactly what you're doing NEVER modify the microwave for ANY reason. You bypass the shielding on a microwave and you could black out WI-FI signals within a few miles... Let alone cause tissue damage or fire risks nearby.