Musical Chairs

For America Online chairman Steve Case, 1997 has been the best of times and the worst of times. His company is at the vanguard of a revolution in cyberspace, with the percentage of US households plugged into online services almost doubling in the last two years (from 10 percent to 19 percent). Better yet, Americans are logging on more than ever, checking e-mail, yakking it up in myriad chatrooms, and browsing for consumer goods at a rate of almost 13 hours per week (up from six-and-a-half