I'm a big fan of podcasts. Big fan.
In any given week I spend more time listening to podcasts than I do music. In Downcast, my preferred podcatcher app for the Mac and iPhone, you'll find a rather long list of subscriptions to a wide variety of podcasts.
Now, most of the audio content I consume comes from these podcasts. Every now and again, however, I run across something that I want to listen to outside of these feeds. It might be an episode of a podcast that I'm not subscribed to or a stand-alone audio file. Regardless, this causes problems since Downcast is central to my audio-listening workflow. Simply put, if it isn't in Downcast, then I'm probably not going to listen to it.
Huffduffer is a service that allows you to turn those mp3 files that you run across on the internet into a customized podcast feed. When you find audio that you want to mark for later listening, simply "huffduff it" using the handy Huffduffer bookmarklet or Chrome extension. This adds the audio to your podcast feed as its own episode. Subscribe to your podcast feed and you're set.
Huffduffer also allows you to tag audio, follow other Huffduffer users, and discover content using search and tags.