http://www.engadget.com/2010/12/05/comcast-internet-down-in-the-midwest-dns-servers-to-blame-again/
http://www.chicagobreakingnews.com/2010/12/comcast-internet-outage-affecting-chicago.html
Use OpenDNS (208.67.222.222, 208.67.220.220) or Google DNS (8.8.8.8, 8.8.4.4).