I see some are having DNS problems and others recommending Googles DNS. I would like to recommend, to those on a Windows system, to give DNS benchmark a try by Steve Gibson http://www.grc.com/dns/benchmark.htm. Using this tool you can find the best DNS server for your connection.

Quote from page
  "The point made above about the suitability — to you — of candidate nameservers is a crucial one, since everything is about where you are located relative to the nameservers being tested. You might see someone talking about how fast some specific DNS nameservers are for them, but unless you share their location there's absolutely no guarantee that the same nameservers would perform as well for you. ONLY by benchmarking DNS resolvers from your own location, as this DNS Benchmark does, can you compare nameserver performance where it matters . . . right where you're computer is."

Mr. Gibson's knowledge of networks has been a great help to me for many years. I hope he can help you, if you are in the need, as well.

By the way he is a Bitcoin solo miner and has done a very nice netcast about Bitcoin http://www.grc.com/sn/sn-287.htm

Cheers