I agree that Perl-based filtering is far nicer than procmail's horrid recipes, which is why I wrote my own Perl filter, parp. (Please note that I am currently making some small changes to the filtering API which will significantly simplify it.)

I am obviously horribly biased, but while Mail::Audit is a pretty decent quick hack, there are a number of things I dislike about its approach, and a number of advantages that parp has over it (daemon/queue mode, folder filtering mode, more powerful OO-based design, automatic regression testing, dynamic learning of trusted addresses, and lots more). I am also intending to provide support for Spam::Assassin in the near future (although I'm still not convinced that SpamAssassin's statistical approach is as flexible in principle as parp's builtin spam-detection heuristics).