||Panther Maintenance Tips|
I use "Cronnix" (http://www.versiontracker.com/dyn/moreinfo/macosx/9478) to manage the periodic schedules. It is a relatively simple app that only really deals with editing ur crontab files in a simple and easy to understand interface.
A major advantage of Cronnix is that u can schedule anything, not just ur periodic maintenance. For example, I use Cronnix to launch, at 7:30am every morning, an applescript i wrote which runs iTunes and plays a random song. I use this as my alarm clock to get up in the morning.
Another advantage is that the latest version supports import/exporting so u can restore all ur crontab settings after a system reinstallation.