I have an experimental bbPress instance which I'm using as a feed reader (it beats Google reader because several of us can annotate and discuss the things it discovers). Something I'm learning quickly is that some feeds are unstable, and this is resulting in dupes, so I'm thinking an admin tool that highlights duplicate articles (based on content or title perhaps) and then makes deletion easy might be useful.
Then I started thinking that it would be a good anti-spam tool. Then I wondered if anyone had developed something like that as a plugin already... or fancied giving it a go... my hands are tied for time at the moment, or I'd hack it up myself.