I just upgraded from OS X Mavericks to Yosemite, and then went through the process of updating my MacPorts ports. Everything went cleanly until I tried to start MySQL. I received the message:
The server quit without updating PID
Searching for an answer gave plenty of articles suggesting that the file mentioned after that error message needed to be created, that permissions were wrong, and other things surrounding issues regarding the pid file. None of those turned out to be the cause.