"Seinfeldia" (Simon & Schuster), by Jennifer Keishin Armstrong Eighteen years ago, in one of the most anticipated moments in American television history, fans of "Seinfeld" obsessed over the series ending its nine-season run and struggled with saying goodbye to one of the most influential, hilarious and successful comedies of all time. In a sense, though, the farewell wasn't entirely necessary. The show has lived on in perpetuity, with reruns broadcast daily in nearly every corner of the U.S.