slow su?

["Ian D. Leroux" <idleroux%fastmail.fm@localhost>]

Since updating my amd64 system to the latest -current two weeks ago
su(1) has been taking ~30s to display the "password" prompt. Otherwise
it works normally.  Other userland utilities run at normal speed, and
even graphical clients like sylpheed are up, running, and responsive
long before su, even if it's their first time being run since boot and
su has been run multiple times (i.e. this isn't a disk caching issue).
A timeout, perhaps?

This could very well be a misconfiguration on my part, rather than an
actual bug.  Before I start trying to systematically revert changes I
made to the system around when this symptom appeared, does anyone have a
hint about where to look?

Thanks,

Ian Leroux