Overall the mainstream media is still more powerful, simply because so many people still rely on them for information. At the same time, there isn't a mainstream organization which doesn't utilize social media. If they didn't they probably wouldn't still be around.
Social media, to me, is far more useful. You can use Twitter to build your own custom newsfeed by populating it with sources and individuals who you trust to provide quality and relevant information. I find it vastly superior to traditional formats and sources. It's faster, more dynamic, and allows me to consume at my own pace. There's no way that doesn't eventually usurp traditional news.
Have you seen the Huffpost Live program? They have a sidebar in which people can live comment on the show, and the hosts of the show will occasionally read some of those comments. It's an interesting attempt to include social media into a more traditional format.