AS ITUNES ROLLS into its second year, it revised some categories for podcasts listed in the iTunes Music Store. Podcasters should change their podcast feeds to accommodate these changes. Until the end of July, iTunes will support the use of the old category names.
When iTunes reads an RSS feed, it captures and stores up to three category+subcategory pairs and then iTunes uses all of them to populate the browse lists that you see when you click the “Browse” link in the Music Store. However, the first category+subcategory pair listed in a podcast feed is the most important, since it is the one listed as the Category field on a podcast page, and it is the only one used to map podcasts into the category feature pages.
Most of the old categories and subcategories are now automatically mapped to corresponding ones within the new system. For example, if a podcast was listed under "Arts & Entertainment > Photography", it now appears under "Arts > Visual Arts." However, three categories have been removed and do not have a similar replacement: "International", "Talk Radio", and "Public Radio". Those categories overlapped with others in the old system, making some podcasts difficult to find.
Changes to categories is a two-week-long process at iTunes. For specific instructions on adding categories to podcast, refer to the iTunes:category section of the technical spec.
Bonus Link: An Irish podcast for the Fourth of July.