From my perspective (~500 employee mail server), greylisting had a much larger impact at the time, thanks to the spambots/viruses attempting direct connection to mail servers. Extremely effective, zero false positives, much lighter on resources. I did use both, of course, so that I could keep a record of how effective the systems were.

Today the situation has flipped. Most of the spam we get is coming from authoritative servers (ie: gmail, yahoo, etc), making stuff like SPF/DKIM/etc next to worthless from a spam perspective (it's still marginally useful for forgeries), while bayes (or in general, trainable) filters are essentially the only thing that can differentiate it reliably.

With a modern setup, you can basically next to zero spam and no false positives. In fact, honest email marketing (ie: mailing lists you've actually subscribed to) are from my experience the only thing that throws these filters off.