The UK Labour Party has a public forum of sorts, known as the Big Conversation. Dean has his Blogging For America thing or whatever he calls it. Bush has Blogs for Bush.
I think these could be great ideas, but I also think they can act like steam valves. I think that, if taken seriously, these forums/sites/blogs could be a great informational resource for government and politicians. I can see internet forums being a great way to do the "notice and comment" period required for administrative regulations. However, if the comments and such are ignored, I can see this being a great way to say, blithely, "of course I'm listening; I have a website, don't you know." It has to be something that is done seriously.