If you happen to publish podcasts on the iTunes podcast listing or are an app publisher on the App Store, listeners or customers can leave comments on the iTunes Store but there's no way to be notified if someone does - plus with all the international versions of the iTunes Store it would take forever to check in on all the different possible places someone could leave a comment for you¹, never mind all the different languages possible.

CommentCast, $5 via PayPal, does some sort of magic to aggregate all the possible comments you can receive.

Via macsparky.com

1. I'm not an app developer so I don't know if there's some back end system Apple has in place for developers to be notified. I'm just a lowly podcaster. ↩