The set-up is interesting.  Obama's health care proposal is detailed on the front page and then there is a tab switching to a blog and discussion page where you can provide immediate input.  It's interesting how seemless it is.  In the future, perhaps each "Issues" page on Obama's website will have a discussion tab so that readers can immediately make comments, raise questions, and enter into a conversation with other supporters.
Most interestingly, there is a disclaimer on the blog.  It reads:

The other thing to make clear is that this blog does NOT represent the opinion of Barack Obama and the campaign.  That would run counter to the whole purpose which is open discussion and debate.   This includes our central posts.  While we are working with the campaign to get and keep this discussion up and running, going forward we will be looking primarily to facilitate a useful, lively discussion.

I think this is a good sign that this is actually meant to be a forum for open and honest debate.  A genuine debate includes the possibility of taking positions that might conflict with the candidate.  We'll see how it develops.
The opening discussion is on a New York Times op-ed about the growing consensus for health care reform.  I'm hopeful though that the blog will address questions like individual mandates, single-payer, etc.
Take a look:
http://www.barackobama.com/issues/health care/
Then click on the My Policy discussion tab.  There are already a number of comments from posters urging Obama to consider single-payer, telling their personal story, etc.