More and more people are using Twitter only as a broadcasting tool. Many of my followers are spammers, bots or people that use automated tools to build followers. The problem is that you may think you have an audience when in fact you’re talking only to a handful of people.
Now, with this feature of creating lists I think many of the problems will be solved. People will create lists with users that they trust, with people that tweet in a constant way, with people that add some kind of value. So, you’ll benefit from other people’s knowledge about other Twitter users. I think this is a big step for Twitter and a way to filter the spam.