Kirk
I was one of the folks having issues on a Mac Mini running Yosemite. I gave up re formated and went back to Mavericks and all was good. Well I just upgraded to a new iMac 27 i7 3.4 with Yosemite and the problems returned which was it freezing up after being idle. I have 3 usb drives that I run . So I tried just running the iMac , no externals, and had no issues. So I unchecked in Sys Prefs ' Put Drives to Sleep when possible" and no more lock ups. Its been 2 days PM being open and it has not locked up. I'll try the link you just put up , see what happens