Just FYI for KDE users -- I recently discovered kcm_cron. In krunner, launch "kdesu kcmshell4 kcm_cron". To set a cron job, first set up the command to be run, and enable all months, then enable either a date in the month, or a date in the week, or all days if you want it to run daily. Then set the time of day to run, and "apply" and you are done.