Thanks to the responses from all and sundry on my torrent question. As suggested below, the Mime-Type is the issue.

I discovered that not only did I have to set up the type on the server side, but also force drupal to list the type in the enclosure field. In retrospect, this makes perfect sense.

Part of the problem is that drupal/php counts on the uploading browser, which doesn't really know about bittorrent, to determine the filetype. I experimented with overriding the default (application/octet-stream) and it seems to have worked. I've whipped out a little drupal module that works well in this context:

http://www.outlandishjosh.com/drupal/torrentfeed/feed.xml

Seems to load up right in Democracy and I/ON.

This is also using the Link element to provide Azureus-friendly feeds as well, although this probably has some bad side-effects in terms of making things clickable for context. I'll keep playing with it in the coming days and weeks.

Thanks to everyone for their feedback. I'll document this and try to spread to word.