As all mail things change I wanted to get some thought if checking PTR DNS records these days is advisable?
1) I do want to use it if it will actually bring benefit
2) I do need to keep false positives as close to zero as possible.
yes, checking of rev-dns is done by most of antispam deployments i've seen.
i guess like with other things [ eg. rbl ] - do not use it to take hard decisions, just add to a score of 'spamminess' counter and mark message as suspected only if general score goes above some limit.
I wouldn't use it to reject outright, but as stated to either weight a spam score or to greylist or some other action.
Also only check on "rdns present", I think you'd have too many false positives if you tried checking for matching forward/reverse dns.