It is very important to reply back to people who leave comments on your blog. I'll admit that I don't always follow my own advice here. I try, but don't always do so well. But it is good to do because it will help you to attract more loyal and regular readers. People who have really popular blogs with dozens of comments being left may not be able to reply to everyone, but until you get to that place it is a good idea to reply back to as many commenters as you can.

One question people often have is should they reply back to the person who left the comment, through another comment left in the comments section of your blog or email them back personally? If you reply back in the comments section there is a possibility that the commenter will never see it if they don't come back to check the blog post again. Using the Subscribe to Comments plugin helps, but it doesn't guarantee that any specific reader has actually subscribed to the comments.

If you email them only and don't respond in the comment section, when other people visit your blog it may look to them as though you never respond back to those who leave comments. Responding both in the comments section and sending each person an email can be kind of time consuming.

Why use the Comment Email Responder plugin?
The Comment Email Responder solves the problems mentioned above by letting you both reply in the comments section and email the commenter back at the same time.

How it works
Comment Email Responder works by creating a small icon of an envelope with an arrow on it next to each commenters name - but only you can see it when logged in as admin. When you click on it, it moves the cursor down into the comments text box. You then reply in the comments section - and the plugin will then also send your comment to the commenter in an email. But - and this is the really cool part - if the person has clicked the subscribe to comments box - it doesn't send them an email. So no one will get 2 emails sent to them.

Installing
The creator of the plugin has a good page describing how to href="http://www.u-g-h.com/wordpress-plugins/wordpress-plugin-comment-email-responder/">install
the Comment Email Responder. Installation is easy, and once activated, if you look under settings in your dashboard you will find a link to the plugin to customize it.

Customizing and Features
You can choose the name, address and subject you want the email to use. You can also write a short message to appear in the footer of the email. I use something like: "Thanks again for visiting my blog and leaving a comment! If you like my blog please consider subscribing to read updates in a feed reader or by email! "

Other
Keep in mind, there are times when you may want to respond to a comment differently on your blog than you would privately through an email. Sometimes I don't use it and instead reply more generically in the comments section and then send a more personal response in an email.

Overall I think its a very useful plugin. Sometimes I still don't reply in a timely manner like I should, but the plugin does make it easier to reply back to people - so I don't really have a good excuse!