If you are having an issue with iTunes, or any other podcatcher, only showing your most recent ten (10) or less episodes and you are using WordPress to feed your podcast, this is the fix for you.
Even if you are also using feedburner, changing this simple setting will allow more episodes to appear in your RSS feed and thus on iTunes, Zune, Miro, etc.
This fix works for both WordPress.com and people who have their own installation of WordPress on their own server.