If you live in a place with limited bandwidth (See: The boonies), you probably don’t want iTunes downloading podcasts all willy nilly. Luckily, there is a switch inside of iTunes to control this, but it isn’t quite as obvious as I’d like.
First, go to your iTunes Library, and go to the Podcasts tab. At the bottom left hand side, you’ll see a button labeled “Settings.” Click it, and you’ll get a new configuration window.
Switch the first drop down list to “Manually,” and the second drop down to “Podcast Defaults.” Click save, and you’ll no longer find iTunes sucking up your bandwidth behind the scenes. Also, you can change the settings for each individual podcast if you’d like. Maybe you want to automatically get the latest Macgasm episode, but you want to wait to grab Apple’s event videos. It’s very customizable, so you’re in good shape.