Podcasting is, technologically, nothing more than using the enclosure field of an item in an RSS 2.0 feed to deliver the URL of an MP3 file which your aggregator then downloads for you.
I was thinking about setting up a development blog for FlickrExport when it occurred to me that you could use exactly the same feature of RSS 2.0 to deliver updates to an application.
For Xjournal, I wrote an embedded Software Update feature to notify users of changes, and it wouldn't yet make sense to remove that feature whilst RSS 2.0 aggregators are not all that common. However, if I were to convert the internal format of that feature to RSS 2.0 instead of Property Lists, people could subscribe to it in other ways.
One big benefit I imagine you could get from this is automatic updating of version tracking sites like Macupdate and VersionTracker. If you embedded the release notes in the body of the item, these sites could poll registered feeds and automatically update the app's notes, release date and download link.
Just a thought.