REDMOND, Wash :Thousands of people swooned in a dark conference hall that felt more like a rock concert when a Microsoft product manager demonstrated the company's latest feature: how to sum numbers in Excel, with the click of a button. "It was literally like Mick Jagger walked out," said Yusuf Mehdi, Microsoft's consumer chief marketing officer, who started as an intern. That was more than 30 years ago. On Friday, the day Microsoft turned 50, the company's leaders and staff gathered at its