※ Beta 6で確認しました

func application(application: UIApplication!, didRegisterForRemoteNotificationsWithDeviceToken deviceToken: NSData!) {
    var bytes = [UInt8](count:deviceToken.length, repeatedValue:0)
    deviceToken.getBytes(&bytes, length:deviceToken.length)
    
    var token = ""
    for byte in bytes {
        token += NSString(format: "%02x", byte)
    }

    println(token)
}