Just a quick note to say that I've installed OS 10.10 on my laptop (MacBook Pro, Late 2011), and so far my sound tools (ProTools 11, Logic Pro X, QLab 3) are running with minimal problems. No, Avid has not certified ProTools to run on Yosemite yet, but since my studio Mac Pro is running Mavericks with aplomb (and will for some time to come), I was willing to jump in and make the switch to Yosemite on the MBP. I had been running the beta versions of 10.10 for a couple months on a separate partition, so I had a good idea what I was getting into.
Your mileage may vary. As always, if you're currently in a project, wait until it's finished to upgrade. And, back yo self up!