In Conversations with brazilian WP users, i had an idea for plugin (or hack) to answer to the comments:
Insert a link RESPOND in the COMMENT area like the image below:
Clicking in RESPOND, they open a window (like the scrap RESPOND in the orkut) for write the reponse;
The WP send the answer to comment autor via e-mail and automatically insert the same text below the original comment in the article, like image below:
Add the feature to send the same text via e-mail in EDIT COMMENT function.
I'm thankfull to insterested programmers.