Hello I have an early 2009 Mac Pro. After installing Yosemite, things were fine until about a week and then the whole system got really slow and unresponsive. I did an SMC reset (shut down, unplug, wait, replug, boot) and all was well again. Three or four more days later, same issue. SMC reset worked just fine...for another three or four days. This seems to continue to recur. Anyone else? Any ideas?