Ask Slashdot: Is Reverse DNS a Worthy Standard For Fighting Spam?

drmartin66 makes it to the front page with this question: "Last weekend I installed a new spam filter server for a client, and enabled connection rejection if the sending server did not have a Reverse DNS record. Since then, I have had a number of emails rejected from regulator bodies that do not have a Reverse DNS record, and are refusing to have one created for their email server. What is your opinion of Reverse DNS records? Are they (or should they be) a standard, and required? Or are they useless for spam fighting?"