Yes, it is a real gravitation shield! Well, not really, but it is a great thing to astonish people at first and then make them remember the electromagnetism they have been taught at school. It is also a great conversation and demonstration piece in a class studying electromagnetism.
Also, it can be done in five minutes if you find the materials.
It DOES nothing, but, to keep it short if a magnet moves near a conductive something it creates electric currents in it. In the tube they go around the circumference of the tube and create their own magnetic field, which repulses our magnet. And this makes it fall 4 times slower.
Step 1: Find the Tube
You need a longish (30 cm - 2 meters, it is perfectly your choice, about 1-3 cm inner diameter ) piece of conductive and non-ferromagnetic tube. Aluminium works well, but before buying it search the house, it is very likely that you'll find it somewhere. I cut a piece of the hanger rack from an old wardrobe.
Step 2: Now the Magnets
Now the hardest, bur not really hard part. You have to find a strong rare-earth magnet that fits in your tube. I really like it with a spherical magnet, but it is left at school, so I used a stack of ordinary ones instead. They should be able to move inside without touching the tube, but there shouldn't be more than 2 mm between the magnets and the walls of the tube (it depends on the strength of the magnet).
Step 3: Finished
Well, everything is now, but before showing it to anyone, it is better to understand completely how it works, otherwise you won't impress anyone that much!
When you are sure you understand the theory completely, stick the magnets inside the tube and have fun!
PS I've tried to attach a file with a totally useless something (and it is in Russian), but there is a wonderful picture there that explains everything if you meditate over it for 15 minutes.