I would like to know which KM actions cause IDLE() to be reset. For example, does the "Type a Keystroke" action reset IDLE()? I suspect it does. I want to use IDLE(), but I have other macros occasionally running in the background, and I suspect these are interfering with IDLE()'s actually tracking the difference between an individual typing on a keyboard and a KM macro simulating that. If so, what other gotcha's are there?
From what I have seen in my personal experiments, keystrokes and mouse/trackpad movements only. Other macros being executed in the background do not interfere with is.
I'm glad to be proven wrong however. 
Thanks.