I prefer just to ignore it. I got a comment once from "anonymous" saying that no one wanted to read my sob story and then they went on to pick my post apart detail by detail. At first I thought I shouldn't lose any sleep over it. But no one had ever been so mean to me. So I decided to write back. I first asked why they would not just leave a name unless they were someone I knew. In that case, how lame is it that they couldn't just admit their problem with me. Then I let them know that for someone who says they could care less to read my drama, they sure knew my story very well. And I asked them to either keep their comments to themselves or say something to me personally. But to call me out on a comment on my blog, where everyone can see it, just seemed childish. Especially since I knew it was just a bitter ex-friend.
After that I just stopped replying to them. Delete the comments and move forward. If it is more of a critique, then take a look at what the person is saying. You have the choice to take their advice or to ignore it. Sometimes it is just easier and better to take the high road and ignore it. I feel like I am constantly telling my boys to just leave each other alone and walk away. Seems like its the best advice there is.
One last thing, don't let the negativity get a hold of you. Try your best to brush it off. Its so easy to let it knock you down and second guess yourself but don't let it! Be strong and be confident in yourself.