I had known of this particular bit of fun long before I actually experienced it. For me, I was sitting in a chair, and the four people put one finger each, one under each arm and behind each knee.
And yes, it works. Four girls I know, who are not terribly strong, lifted me up. How did it work? I don't think it was diamagnetism. What happened was that the ritualistic part of it helps the participants concentrate. The positions of the fingers is also important, evenly balancing the load.
Still, they only used a finger each! Well, I'm sorry if it sounds anti-mystical, but your index finger can lift almost as much as your hand can, within reason of balance and grip and such. Using two fingers, as erevapisces's story goes, provides even better leverage.