text: Usher Leads American Music Award Nods LOS ANGELES - R B casanova Usher, whose album "Confessions" steamed up the charts with songs about sex, affairs and breakups, received a leading four nominations Tuesday for the American Music Awards.    Many categories included last year's winners - Toby Keith, Tim McGraw and Linkin Park - and previous nominees Beyonce, Avril Lavigne, Norah Jones and R...