I had two major problems I wanted to fix with iTunes podcasting. One was that it didn't update them if I happened to quit the app (unlike Safari, which uses SyndicationAgent to monitor feeds). The other was that the built-in scheduling only makes three huge jumps between hourly, daily, and weekly. The combined problem being that if I happened to quit iTunes before a nightly update, I wouldn't have anything waiting for me until I noticed the problem when I wanted to sync my iPod in the morning ... and then the scheduling was wrong for every day afterwards.
The solution is a simple iTunes AppleScript:
tell application "iTunes" to updateAllPodcasts
You can use iCal, or any other scheduling app you like, to run it when it makes the most sense for you. I use cron with the following entry:
00 5,17 * * *
osascript -e 'tell application "iTunes" to updateAllPodcasts'
So now I have podcasts downloaded and waiting for me both before I get up, and before I get home!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20061219003616685