For the past three years, South Korea's Hyundai Motor has been the fastest-growing automaker on the planet. Driven by increased sales in the U.S., China, and India - not to mention in its home country - it has boosted production by a third and is poised to pass DaimlerChrysler and join the ranks of the world's top five auto manufacturers. Unit sales were up 16% in the first quarter, leaving industry observers wondering whether anything could slow the company's growth.