Google Reader is already trying to do this with its social features. So far, not particularly well: I just use a combo of RSS and reddit to find things which interest me.
I use TweetDeck. I have found it to be an incredibly powerful application. At any given time I have about 5 columns up and I see trends and interesting content on the those subjects in real time. The noise is already reduced a lot by the more pertinent info getting retweeted more making it easy to spot.
For example, during PDC, I had a #PDC column up, and I almost completely effortlessly kept up with all the latest info. A #monotouch column is a more permanent member of my collection, it alone has me staying on top of that community, again, just about effortlessly.
I guess the other part of this is also that on Twitter I mostly only follow... well, my actual friends. The whole "follow 10,000 people and get a client app to sort what they're saying" workflow just doesn't appeal to me, and it seems that in order to do what you're doing you'd have to follow a huge number of people.
That's the beauty of TweetDeck. I only follow about 20 people. In TweetDeck you can set up additional search columns and it will show you tweets across all of Twitter (updated in real time) that match your search. IMO TweetDeck takes Twitter to another level (and actually makes Twitter useful :) )
