Generator maker Generac Holdings (GNRC) jolted its investors Wednesday with its announcement late Wednesday of a 10 million secondary offering by one of its large shareholders. Shares tumbled 5.5% in response intraday on the stock market today. Investors in Michael Kors (KORS) know the feeling. The fashion house was strutting higher on last week's blowout earnings. It hit a new closing high Tuesday at more than triple the December 2011 IPO price.