Oh man, another place for me to waste time. This seems very cool, I'd love to see more sources added to it. I agree that the source and topic should be made more easily discernible. Once you add more sources, I could see it getting confusing.

A daily email digest would be a good idea for many users. I like to get involved in a discussion, though, but the digest would have to be sent after the discussions are over. Maybe a section for "rising" discussions if that's possible with how you've designed this?

I'll definitely try to use this next week as my time-waster.