It is no secret that Comcast DNS servers are at times terrible: http://blogs.computerworld.com/node/5672
At work we've found that for some reason we couldn't reach google, gmail, or all of our google products. This happened several weeks ago and was worse on Macs and our Linux machines.
We all switched to using OpenDNS, instructions here for Ubuntu: https://store.opendns.com/setup/operatingsystem/ubuntu , and not only did our web-surfing get way quicker, but we were able to reach google without a problem.
