If you use a bluetooth headset and did update your Apple Computer to Yosemite, you probably also discovered that the sound starts to lag after a few minutes or when the computer just woke up from hibernation mode. With OSX 10.10.1 being the latest version, there is still no real fix available. The only option right now is to install the latest beta version of 10.10.2. I did that a few day ago, the bluetooth issue is fixed and I also did not experience any other problems.
All you need to do is switch the App Store to the beta channel by copying the following instructions into terminal and enter your admin password:
sudo /usr/sbin/softwareupdate --set-catalog https://swscan.apple.com/content/catalogs/others/index-10.10seed-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog.gz
Afterwards start or restart the App Store and search for updates. It should give you the option to install 10.10.2 (Beta 3 / Build 14C81f) just like any other OSX update. It takes about 5 minutes to download and 10 minutes to restart and install. The bluetooth audio lag should be gone.
Update: My version numbers where .1 too high, so I changed that back to the real numbers.