It is now 2½ years since my last post on greylisting, and over 3½ years since I reluctantly started to use this spam prevention technique. I am pleased to report that greylisting remains as successful as it was on day one.
In fact, the situation has even improved since that last post 2½ years ago: The overall spam rate has dropped from 36 to 14 messages per day! It is unclear whether the reason for this is a world-wide decrease in spam mails, or a decrease in "quality" of spam mails, i.e. fewer spam mails make it past the greylisting wall. I don't need to know the exact reason, though, to feel happy about the result: Due to the low overall spam rate, on average only 1.4 messages per day now make it into my inbox. Wow, these days I can even leave my mailbox unattended for a few days without getting flooded - isn't that great?! (compare the current situation to when I only had Spam Assassin and, at the peak, my inbox was inundated by more than 40 new spam messages per day).
For more statistics details, see this wiki page.