After apt-get upgrade this morning, my Ubuntu 12.04 web server does no longer resolve a domain name hosted on it.
I also received the error message:
"resolvconf: Error: /etc/resolv.conf isn't a symlink, not doing anything."
I found this question Network Manager not populating resolv.conf but the solutions provided there did not resolve the problem.
Creating the symlink in fact caused websites to load very slowly, so I assume there is some sort of (reverse?) DNS lookup not working, when I create the symlink.