Yes. The ability for the average citizen to gather, analyze and publish their own news is paramount in ensuring the main stream media does their diligence on their own news stories. I would imagine the major news network executives would not want to see their headlining story proven wrong by the average citizen. I think that overall, the positive impact of citizen journalism is keeping the main stream media honest.
Web 2.0 is the same as social media. Social media such as Facebook and Twitter are Web 2.0. Social media is important to citizen journalism because of the social beings relating to each other. The more that the social beings relate, the more relevancy for the use of Web 2.0.