Less than 24 hours into using Yosemite and I had my first complete system hang with a small piece of audio looping. Not only is it unstable, it takes a lot longer to login than previous versions of OS X.
I have had no issues with any of the Public Betas or the clean install other than yesterday...
Came down to my office after leaving iTunes playing for a couple of hours to the sound of the fans going crazy on my rMBP. I pressed space to wake the computer from sleep and had a black screen with the folder and question mark icon.
No idea how this happened and hoping it was a random one off. Held the power key for a forced shutdown and restarted with no issues so far. Maybe a few ghosts in the system for users that need a little attention?