Good news for me at least. I just installed the Yosemite update that came out this morning and it fixed it. That is a relief.
If I start the laptop with all the displays connected it still just mirrors all 4 screens with an ugly low res 4 by 3 login screen. If I unplug all the displays once it has started running they work fine.
Fred Knack
Motion Graphics Artist & Final Cut Pro Editor & FLASH Programmer
Portland, Oregon
http://www.fredknack.com