Very comprehensive, informative article. I agree it's definitely time-consuming going and commenting on various blogs that are related to your industry, but it does ultimately pay off.
In this 'Social' world in which we live in, dialogue between both individuals and communities has become very natural, almost obligatory - look how emotional and sometimes confrontational people can get about whether that song is any good on YouTube, or the popularity of hashtags on Twitter. Whether a big or small issue people want to be heard - for better or worse it's one of the closest things to true democracy we have (when censorship doesn't come in too strongly, although I see the need for it if people are just being abusive and counter-productive to conversations).
I believe businesses increasingly have little or no choice but to join these conversations. Purchasing has become a more vocal, personalised experience - and people can raise or take down a brand within in a matter of a few minutes, that is how immediate Social communication is, and how important it has become. So get talking to your audience, not just on blogs but on anywhere people have reviewed either your product or service (in a negative or positive way alike), and don't be afraid to engage with them - you will gain more respect from them than if you remain in that impenetrable Ivory tower. So start getting down with the people!