PAM

[.:B:.]

Slim can use it too:

[stijn@hermes ~]$ ldd /usr/bin/slim |grep pam
libpam.so.0 => /lib/libpam.so.0 (0xb7e1f000)

This link explains how PAM works.

[thenktor]

but if you have pam, the password prompt after issuing "su" takes a while to show up, but without pam it's instant.

No delay here

[gapan]

As far as I can see there is nothing that a desktop user would care about in using pam. Even if that "ssh only certain times of day" sounds nice, it can be done with simpler ways anyway (crond switching ssh service on/off for example).