I recently switched from a mysql.com implementation of MySQL to MacPorts on my local, and the Drupal sites would no longer load.
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.
Have you moved a Drupal site to another server and received the error 'The directory sites/default/files is not writable'?
I recently needed to test out some new code on my local version of a client's site. I ran into a problem, because keys and information that I needed for the testing were in the live version of the database, but not in my version.