I thought I might as well start a new thread to report any info I find worthy to be so on the IDE front.
1.6.6, released on Nov 3rd, seems to be best left alone according to early comments:
https://blog.arduino.cc/2015/11/03/arduino-ide-1-6-6-released-and-available-for-download/
So stick with IDE 1.6.5 for now folks, no matter how tasty the Serial Plotter seems to be!