Now that people and organizations have been blogging, setting up Facebook groups, and participating in social media generally, they have had an opportunity to gather feedback. And some of that has been and will be negative. Alot of that feedback is valuable and worthwhile responding to. Other feedback (e.g. from trolls) is not worth your while and indeed may have been actively managed.
If you feel this applies to you, read this mashable.com post, HOW TO: Deal With Negative Feedback in Social Media