Quite, at least in 10.1.5. I have been meaning to test this for awhile. I logged out of my OS X machine about 2:30 this afternoon and kept an eye on the load graph. Without Aqua running, utilization drops to UNIX-like levels (ie, 0.0).
Even with the monitor off and no one sitting at the machine, it uses 20 – 30% of the CPU just being. As it is now, I still have network services (I have an NFS volume mounted from it on my laptop), and I can quite happily run interactive processes on it.
Seems like a good argument in favor of logging out at the end of the day.
Update: I discovered it was Classic, not Aqua, that was churning away. So leaving an Aqua session logged in, annoying and non-secure as that as that may be, won’t be a resource drain.
PS: that long load spike from 4 AM to almost 6 AM is a fink update I have in root’s crontab.
source /sw/bin/init.csh; /sw/bin/fink selfupdate-cvs && /sw/bin/fink update-all -y
It will update fink itself from CVS, then update any installed packages from the latest CVS checkins.
PPS: I keep this graphs here.