A few suggestions:

There needs to be a way to sort the results by source so people can see only mentions on twitter, digg, blogsearch, etc. Currently it can be tough to tell where any given conversation was found.

It would be helpful to have negative filters for removing false positives. Some brands have similar keywords, so it's annoying to see the same irrelevant topics coming up.

The positive/negative filters need some work. About half the results in the negative tab were actually positive in the test I did.

You're tracking the keywords by sucking in RSS feeds for search queries correct? You might have a challenge convincing savvy individuals to pay for a service they could basically recreate in an hour inside their own feed reader.