I find the blog commenting space to be one of the most fascinating battlegrounds on the web right now. If you are trying to build a distributed business, there's much to be learned from the trials and tribulations of companies like Disqus, JS-Kit, and Intense Debate as they attempt to build out a footprint by pushing a feature to existing blog communities.
I've written extensively about how I believe that there are all sorts of features that can be won on a cross domain basis. By studying the pioneers in blog commenting addressing issues such as the SEO-ability of content, less than friendly host platforms, login, and universal profiles, perhaps providers of other cross domain features can gain a leg up.
Intense Debate is a company that I don't know very well, probably because they're not local to SF. They came out of TechStars (Colorado's version of Y Combinator) and is often evangelized by Brad Feld.
Here's an interesting interview with Intense Debate founder Jon Fox on Center Networks.
