Thanks again for your replies. I have been referencing the same spec.
I would expect ID3 tags to be the default authority for item-level meta and any web-app logic an override. This comes from a perspective of work flow; the file is managed locally before uploading to the server. Why do the work twice? I can see how some would prefer to set item author to post author but that should be a an override provided as a convenience, what do you think?
I see in the iTunes spec that item category isn't supported; didn't notice that before. I've been using the podcasts I subscribe to as models; they all have item category set to Music even when they have multiple channels. Would love to know how they do that. Given the choice between displaying the WP post category and being blank, I'd go with blank.
#1,3,5 (Subtitle and Summary)
I've just discovered that with Feedburner's Smartcast feature turned off things work a little better:
channel subtitle (itunes description) = Subtitle (pod-chan)
channel summary (itunes 'i' in description) = Summary (pod-chan)
item subtitle = truncated post text
item summary = post text
When Smartcast is turned on the channel subtitle gets set to Summary.
So working with Smartcast off for the moment, things look like they are behaving the way you built them.
I would argue that 250 character have no place in the iTunes Description column. How do you read it all? Apple says, "The subtitle displays best if it is only a few words long."
Also, your logic for item subtitle sets unfortunate demands on the way posts are written. Rather than begin the post with some prose and have these first 250 chars appear as irrelevant text in iTunes Description for that episode, I have to begin my post with a summary (ie, "This week we focus on the music of SoAndSo") and even then the balance of 250 chars appears in iTunes.
Would it be difficult to add a text field for item subtitle? If not, how about set it to the value of post excerpt rather than truncating the post body?
As for item summary, I can understand the logic for including the entire post text, but can we filter out the WordPress markup such as 'caption' and 'audio' (the second being markup for wpaudioplayer)?