I previously posted on how to be notified of a new comment in Drupal 6, but there is a slight change you need to make to the settings if you want it to work in Drupal 7.

Instead of using this snippet

Hey, there's a new comment on %title.<br /><br />
 
%node_url <br / ><br />
http://www.example.com/admin/content/comment<br /><br />
 
-Drupal

The syntax for token replacement is different. You'll have to use the square brackets and prepend the token replacement values with comment like this

Hey, there's a new comment on [comment:node:title].
 
[comment:body]
 
[comment:node:url]
http://www.example.com/admin/content/comment
 
-Drupal