Im running the latest PS CC version on a 3.5GHz i7 imac with 16gb of ram and 2gb of GPU ram running the latest version of Mavericks. Every time I try to mask and them use a brush to hide or reveal, I get the spinning gear. It has never happened before. Makes all the editing I have to do take twice as long as I have to wait for the machine to catch up with what I've done. Very frustrating.