I implement greylisting on my mail servers. I'm not too picky, but I am having a lot of luck blocking spammy messages before recieving them, doing it.
The wonderful thing about greylisting is that -- to be standards-compliant -- you have to resend your message to me after a sensible delay. The RFC recommends 4h, AFAIR.
So, if you can't deliver your mail to me because you drown in temporary failures mentioning greylisting, please consider fixing your broken setup before ranting to me at my regular address: skrewz@skrewz.dk (... which you probably won't be able to reach through your normal setup)