"Come to me!"
On a quiet Sunday morning in Silicon Valley, I am standing atop a machine code-named Ginger--a machine that may be the most eagerly awaited and wildly, if inadvertently, hyped high-tech product since the Apple Macintosh. Fifty feet away, Ginger's diminutive inventor, Dean Kamen, is offering instruction on how to use it, which in this case means waving his hands and barking out orders.
"Just lean forward," Kamen commands, so I do, and instantly I start rolling across the concrete right at him.
"Now, stop," Kamen says. How? This thing has no brakes. "Just think about stopping." Staring into...