Apple organized a whole slew of standard categories or genres for podcasts, when they defined the itunes RSS namespace for podcasts. This helped discoverability of podcasts, as podcast applications and indexers can let users search or browse by genre, or make suggestions based on genres users seem to prefer.
Apple seems to have done a pretty good job at this. It's not obvious that "podcast genres" are meaningfully distinct from "blog genres". We could, of course, invent some analogous kind of categorization just for blogs, but why? As Dave Winer hath writ:
Fewer format features is better
If you want to add a feature to a format, first carefully study the existing format and namespaces to be sure what you're doing hasn't already been done. If it has, use the original version. This is how you maximize interop.
Podcasts got a huge lift from what was originally the blog-centric RSS format. Why haven't blogs adopted podcast-RSS best practices to get a lift right back?
There's a potential issue that some applications may use the presence of itunes RSS tags to imply an RSS feed is for a podcast. But that's pretty dumb. If applications expecting podcasts import blogs without soundfiles because they use this heuristic, well, bad on them. They should fix that. When blogs do contain some posts with audio <enclosure/> elements, then arguably they are podcasts inter alia. Client applications should use intelligent criteria to decide what they want to consider suitably a "podcast" or "podcast episode".
It strikes me as a good idea to make use of good ideas from the itunes (and podcast) namespace for blogs and other RSS applications.
Starting, perhaps, with itunes:category.
Apple defines itunes:category as a channel-level element that permits multiple entries (you don't have to be just one genre), and nested entries for subcategories. Seems pretty good!
What do you think?