So we are fully aware of the age old chicken-egg problem that all small start up projects face online these days. We need our users to add content in order for there to be content for our users to use in order for rbutr to have any value. This is a real problem, and our primary focus at this point.
I have just made a video about adding content to rbutr, which will hopefully help our alpha testers find content to add, and this approach is basically the best strategy we have come up with at this stage to add content – find rebuttal content creators, and browse their material. Subscribe to them, and whenever the reply to something, Add it!
It is a bit annoying, but until we get a few hundred users doing this – starting at the conclusion and working backward adding the content to rbutr, rbutr won’t be able to deliver on its promise of enabling people to read online discussions ‘forwards’.
Shane

Well, there’s also the “link:” keyword in Google (and some other search engines) that will let you find articles that link to a given article. But of course some links signify agreement, not rebuttal.
If you do start with the rebuttal sources, how do you identify (in an automated way) which link in a given post is the one being answered? It’s not always the first one, depending on the style of the blog.
One thing I looked into was using meta-data in the posts themselves that might signify whether a given link might be a “disagreement” link. One might be that the link was the only one that was NOFOLLOWed in the post. (That links to my justification for skeptics to use NOFOLLOW.
Another way would be to encourage bloggers to use microformats like hReview or perhaps an Atom in-reply-to element to indicate the item they are rebutting. Like nofollow, some of these could be quite easy to implement, and would allow certain blogs RSS feeds to be pulled in wholesale.
And not only do inbound links indicate a range of reasons for linking (agreement, reference, commentary etc as well as rebuttal) but also, these links are only registered when they are indexed. If you are reading a recent newpaper article, and a relatively small blogger has written an awesome rebuttal to the article on the day it was published, Google won’t even find it. Our goal is to get in to the bloggers heads, and get them to use the app themselves as a way of getting in front of their real target audiences – the people who are reading the article they disagree with.
So we have ideas for creating a wordpress plugin, for example. If we could perhaps use a rel tag for ‘rebut’ or something like that (the tags you linked too could equally be used), and make a wordpress plugin which finds that rel on a published post, and automatically adds it to rebutter and then renders an image on the rebutting post “Vote for this rebuttal” – we manage to make the process of adding rebuttals easier for authors who write them, AND gain some automated advertising for rbutr (helping grow the community), while also allowing the author to promote their own rebuttal (in much the same way as people promote their own material throug stumbleupon, reddit and digg)