I share the point of view of the last reviewer, but I've noticed something in Leopard (on an iMac G5):
The routines seem to run, be it with Mac Janitor or Onyx, but if you look at the logs in the console (/var/log/daily.out, monthly.out and weekly.out), they don't seem to be changed after running the scripts. (the daily log was full of things from one year ago that weren't erased when I was running the script)
So I ran them in root user account after having trashed those files from within the Console and I got new clean logs...
I don't know if it's useful or not but that's the way to do it. ;-)