Presto made himself well known in the Las Vegas area (particularly to the police department) by performing this spectacular feat of street magic on the famous Las Vegas Strip. Recently, Criss Angel has resurrected this effect, albeit using a slightly different method
The magician selects a spectator who wouldn't mind being levitated. The magician stands behind the spectator and makes magical gestures. The spectator begins to rise into the air, even though the magician's hands can be seen at all times.
This effect requires the use of an "instant stooge" -- a spectator who is willing to play along as a magical assistant. The magician looks for someone who seems like a team player, is wearing pants or a skirt, and doesn't weigh a whole lot. Spectators on crutches or in wheelchairs should probably not be considered. Bending close to the potential assistant, the magician asks if they will "play along" to "have some fun" with the rest of the crowd. Note that in most states, if the spectator answers "yes" this is a legally binding contract and they may not divulge the secret of you effect ever at any time, so long as they live, under pain of significant fine, possible jail time, and a felony conviction.
Once all this "paperwork" is out of the way, the magician stands behind the assistant. With a quick practiced gesture, the magician reaches into the top of the assistant's pants or skirt and hooks thumbs beneath the elastic of the assistant's underwear, one near the right hip and one near the left hip.
From here, it's just upper body strength and acting.
The magician uses the thumb hold to lift the spectator while keeping the fingers spread wide to the assistant's side, giving the appearance that they are holding on to nothing. The assistant can be made to rise, lower, fly from side to side, and (with a little practice) spin like a wheel of fortune.
When the trick comes to an end, the magician lowers the assistant slowly to the ground and makes sure that there the assistant's clothing is not in a telltale "wedgie" formation while disentangling the thumbs.
Note: This trick has a few difficult aspects. First, it is a bit angle sensitive and can only be performed for an audience directly in front of the magician. Second, once in a while an assistant begins freaking out and/or screaming, possibly due to a fear of heights. And third, there is always the danger of choosing an assistant who is not wearing underwear. To minimize this possibility, avoid selecting attractive young women wearing shirts that show their bellies and unwashed older men wearing shirts that show their bellies.