I updated my MacBook 13″ mid-2012 from Mavericks to Yosemite and everything was perfect, until I recognized that I couldn't check my YouTube feed.
I tried again and again, but it didn't work.
I tried it with other DNS Servers like Norton Security Free-DNS or the Normal Google DNS, but nothing happened.
In the end, I tried to use the Google IP in my Browser, but that only worked always for one link.
Running the Ping - Google.com results in
cannot resolve google.com: unknown host