I agree that media does influence socio/political structures. In my view, public opinion is important and is experienced most through it's dynamic relationship with media in the following ways:

1) Media as a force in influencing public opinion. The story of oppression, silence and hostility in media outlets have been successful in catalyzing previously disinterested or unaware parties to engage in socio/political discourse and political action, especially in places that allow that type of participation.
2) Blogs and other internet forums are being taken seriously by traditional news services and media. This, to me, suggests that public opinion has found another way of being heard.

When public opinion differs from media portrayals, which I think it often does, the expression of public opinion suffers and becomes virtually unheard. For instance, when looking at popular American movies in 2007 I would not expect to find a mirror of traditional family values despite polls suggesting that it is of importance to Americans. However, climate change would be an example of a media movement that shifted public opinion and has become a topic of political discussion. Do you see public opinion as having a more independent or influential voice than this?