All of you naysayers out there (I'd be one too if I said it but I won't, read on to find out why) are making a terrible, terrible assumption: that every mail system admin out there will jump on the greylisting bandwagon and implement this.

Back in reality, a lot less than 0.01% will actually implement this technique, especially after reading this thread. So, it's a non-issue. Greylisting is dead.