Excessive delay after typing sudo?
Looks as though the optional pam_ck_connector.so is hanging not only sudo but other auth processes (eg roundcube/dovecot/imap).
From here by erikdhansen (http://ubuntuforums.org/member.php?u=36598)
(Copied in case ubuntu reorganise their forums!)
"Re: SSH Login takes long time (no DNS Problem)
So I was having this same problem and it wasn't the DNS issue that everyone points to. It ended up being a problem with PAM.
I was able to verify this by noting that telnet logins also took a long time to establish and PAM appeared to be the culprit there, as well. However, cron didn't see delays with PAM when it ran. Looking at the difference in PAM configurations for cron vs. sshd revealed a line in common-session that turned out to be the problem.
and here are more per-package modules (the "Additional" block)
session required pam_unix.so
#session optional pam_ck_connector.so nox11
It was the PAM CK connector that was introducing the delay. Commenting out that connector got rid of the delay in my case."