If you create a podcast it's important to pay attention to Apple's new iTunes requirements. I've cut and pasted them below:
Dear Podcast Provider,
New Cover Art Requirement
iTunes has been completely redesigned and there are new requirements for podcast cover art. To be eligible for featuring on iTunes Store, a podcast must have 1400 x 1400 pixel cover art in JPG or PNG format using RGB color space. The image URL must end in ".jpg", ".jpeg" or ".png" and the server hosting the image must allow HTTP HEAD requests. See our technical spec for details.
Server Configuration Requirement
Podcast streaming playback on iTunes requires all hosting servers to enable Byte Range Requests. Please confirm your hosting servers have this functionality enabled. If you work with a third-party hosting service, please contact them to confirm this functionality is enabled on their servers.