Comcast's name resolution services have been trouble for some time, as far as I know. What I discovered lately just goes to show how bad the problem truly is.
I use an OpenVPN connection for some business of mine. Behind that connection runs a set of DNS's used to serve both private and public IP's. So clearly we are talking a connection via an encrypted hop - not the fastest, you would think. Yet when I establish it my browsing experience goes from anemic to flawless! And mostly, I bet, this is due to the DNS being responsive - unlike the Comcast one which is so bad that sometimes even loading a fairly common, local webpage such as Boston.com can get majorly frustrating as you are waiting for it to move from one element to the next.
I guess we need to find a way to create some real competition for these dinosaurs - or else they will probably never start feeling like they have to do any real work.