I upgraded both my MacBook Air and MacBook Pro to Yosemite over the weekend and I saw that both my laptops were unable to connect to internal systems at the office. For instance, I wasn't able to access my QA server by going to http://qa.cappex.local. I, however, was able to access the same server by going to http://qa/. Also, I saw that while I wasn't able to ping qa.cappex.local, nslookup worked just fine.
I Googled around for a good 20-30 minutes in search of a fix to this problem and came across an answer in https://discussions.apple.com/thread/6611817.
Executing the following command in my terminal resolved the DNS issue on both my Macs:
sudo discoveryutil mdnsactivedirectory yes