Currently there are several articles like the one on Arstechnica that complain about the DNS resolver in OS X 10.10. Amongst others they report issues with name resolution per se and Bonjour machine names that get changed. Many of this posts then suggest to replace the new discoveryd with the legacy mDNSResponder service.
This post acts as a warning: Never ever replace core system components!
By following the instructions to replace discoveryd you are completely on your own. By replacing such a vital system component you can introduce all kinds of bugs. Many of those may not even look related to name resolution but are triggered by some strange side effect. Furthermore I’m pretty sure Apple does not test their updates with this Frankenstein-like system configuration. Last but not least you may even introduce security problems.
Even if there are bugs, which is inevitable, please report them to the developers and wait for a system update to fix them. You simply don’t know what problems you cause by doing otherwise.