A spoon was placed in the microwave. No sparks were noticed but now when you use the microwave for more than a minute, there is a smell of electicity. The microwave still heats food.
No. If the microwave still heats, it's not ruined. Here's a nice video of the aluminum coating of a CD being burned off by a microwave. Notice the plasma balls rising to the top of the oven. They'll produce ozone, which has an electrical burning sort of smell. You can get the same plasma balls using a match or candle. That doesn't wreck the microwave either; makes a heck of a scary sound though. You can also smelt aluminum, or even silver and iron in your home microwave without damaging the device. If you make a habit of doing things like this, it's best to have a dedicated oven for the job, as melted plastics, heavy metals, and metal oxides do not mix well with food.
Washing out the microwave's insides should take care of any residual smell for you.
What does electricity smell like?
Honestly I have no idea what you mean with a "smell of electricity". :)
If you mean it smells of smoke or burning, then there is something to be concerned about. Metal can but won't with 100% certainty reflect microwaves or damage your microwave. Mind you it is still a very bad idea to put metal in a microwave, it just does not spell its doom right away.
If you do smell burning or smoke, you need to have it checked, as it is possible microwaves were reflected back to the magnetron and caused damage. Although if it still functions and heats food, this means the damage is most likely minor and prolonged use will simply fry a cable or something and you will have to replace it.
EDIT: I am sorry to do this, but i don't have 50 reputation to comment on "Wayfaring Stranger"'s answer and i feel i have to say that NO appliance is working fine and is completely undamaged if after use it smells of electricity (or anything but food). Although the damage or problem could be minor, you might want to have it checked out just in case or to prevent potentially having to buy a whole new microwave in the near future.