Even better than having it only run when no one is logged on is to use the "pause if running" option, which is what I do.
Just add the following line to your .ini file and restart the service:
[triggers]
pause-watch-plist=taskmgr.exe
As soon as you start taskmanager... within about a second... the client will pause. Then, after you exit taskmanager it will start again. I use this with all of my user machines so that no one freaks out... in fact, no one has noticed!
Joe