A backend update yesterday afternoon (July 27) borked the podcast feed until this morning (July 28). It should be operational again now.
Also note this beta podcast feed:
...is a podcast feed in the strictest sense. We're including enclosure metadata in each feed item so that your Podcatching application can automatically download the audio content. We have not implemented the new itunes-specific metadata tags.
Please comment here if you continue to have problems with the feed. Thanks.