In keeping with my earlier promise to start posting functional yet somewhat incomplete code, here's a link to a relaydelay front end. I've posted some of this code before, but there are some new additions.
Modifications to relaydelay.pl to permit logging via syslog, specifically for graphing
The included relaydelay.pl also incorporates the daemonizing patch and my domain whitelisting patch
A daemon script that eats the syslog output via a fifo and creates RRD graphs of greylisting stats
A view PHP script that permits non-privileged views and searches of the relaydelay database.
Most of this code is the result of a joint effort between myself and Matt Prigge. This isn't an official package, but there is a README in the root of the tarball that will get you started, and some assembly is definitely required. If there's enough demand, I might throw together an installer and other associated code, but for now this is it.