Its a fact that with blogs expanding at the rate they are you can just about find any sort of comment about anything. Often a rant, others well balance reasoning but all accessible - all you got to do is spend the time finding it.
And that is the problem - many are only read by the writer (like this...?). PR can't spend every minute collecting and answering every comment. I decision has to be made on significance. It is under recognised at present but a soon to be valuable skill will be isolating your key online opinion formers. You might think you know who they are but its a fast moving world out there and it has never been more important to sample your customer/stakeholders about who they listen to.
PR Week did an interesting item on this recently but as is often the case seemed to just state the obvious without actually digging into what was working for people and why.