I've attempted to draw levitating people a couple of times and have found that doing so can be incredibly frustrating. They always end up looking like they're jumping, lying down, or just plain wrong posture-wise. I can't quite manage to get that feeling of weightlessness yet.

However, this girl certainly has: http://yowayowacamera.com/

That's the blog of Natsumi Hayashi, who have uploaded daily photos of herself 'levitating' - aka, jumping until she gets a shot in which she appears to be unaffected by gravity. Aside from having some rather stunning photographs, I found it to be great for practice reference.