I heard that in the musical, Bert actually dances...on the ceiling. Upside down.

WOW.

Does anyone in the world know how this is possible AT ALL?

I was thinking magnets...really strong magnets...

You're kinda right - what happens is that in Step in Time he walks up one side of the proscenium, dances his way (upside down) across the top of it, then down the other side. It's just done with regular people-flying apparatus, he's in a somersault harness with a wire clipped to each hip point, which is essentially a swivel point. I suspect that there is a wire either side of the prosc, so that he's centred on it; the wires are tracked and move along the prosc with him - probably not automated, there will be crew members in the wings pulling ropes. When I saw the show, I was right around one side and I could see Bert being clipped onto the flying gear in the wings.

Yup. You can see the platform swinging back(well, the wires that were holding him swing. The platform just glides.) across afterwards during the slow reprise. They hang him up upside down in the wings for a while first to acclimatise him to it.

it looks really neat

It's not an amazing effect reeeeeally.

He wears a fly harness with a swivel point on his hips, they're really big ugly black wires and are very clearly visable, but it's still impressive to see him go up the wall and ceiling.

Yes, he does. When I went to see it, I was like:
He's hooked onto wires, but still... I give him huge props for doing it--it looked really scary!

I went to the stage door afterwords to get autographs, and I was talking to the man who played the banker. He asked me my favorite part of the show, and I said the tap dancing. Told me not to try the upside down part at home. lol.

I saw this show Saturday night, and I was in row 11, so I saw exactly how it was done. (Well, almost.) During "Step in Time" he goes off stage and comes back on with two wires, one on each side of him. Then he starts walking up the walls of the sage with the wires pulling him up, (And I think he helps pull himself up as well) and once he gets to to the top, he steps onto a moving platform which glides across the stage. He doesn't walk, he just stands in place and tap dances.)

Really? Huh. It didn't look like the proscenium was moving when insaw the show.

It's a nifty effect when he actually gets across the ceiling, but the hip swivel points are impossible to miss.

but still i guess it's pretty awesome tricks WOOw