Sender ID Ineffective Against Spam ?
They determined that e-mail coming from an IP valid for the sender address may well be spam. Of course it may - the SPF record is only useful in connection with a white list of addresses or domains. But once white lists can be trusted, we can apply stricter filtering on email from non-verified addresses.
They further complain that validating the sending IP yields 8.6% false positives. Maybe so. But these false positives are mainly from large organisations - they are the ones who send mail from an IP different from the one listed in their MX record. Once a significant number of receipients require IP validation, the senders will get their SPF records in place within hours.