I run Ubuntu 12.04 (yes I enjoy Unity!) and as a consultant I go to many different customer sites. I had recently run updates so I thought something got screwed up on my machine or it was slowness at a site. After a couple of days, updates, and different sites I noticed no change so I investigated.
In 12.04, DNS was changed quite a bit and uses something called resolvconf now. This actually works much better with some VPN networks I connect to in terms of split tunneling so I've been happy with it. I had to change some scripts I use on my machine for stats but that wasn't a big deal. No more /ets/resolv.conf or so I thought.
I checked my DNS stats and everything checked out.
nmcli dev list | grep DNS
I finally looked at resolv.conf and found entries in the file for a site I had been to a few days ago. Clearly my machine was trying to hit those DNS servers, timing out, and finally using my real ones. I manually edited resolv.conf to remove those servers and I'm blazing again.
Not sure why the reslov.conf file wasn't clearing out but something to keep an eye on.