Plain old greylisting can yield many false positives, but recent implementations of milter-greylist for example will not greylist messages that validates SPF. It helps *a lot*.
The question is: does it only help "a lot", or is the result "zero false positives"? I personally don't believe SPF was a good idea, so for me it's not clear that it fully solves the problem mentioned by Jaroslaw Rafa.
Gregory
