Should you be sending thank you emails to people that comment on your blog?
Jennifer Chait at Freelance Writing Jobs doesnt think so. Why not?

If all bloggers sent thank yous, all commentators would have a lot of email spam.
It is a waste of the bloggers time – they should be working on quality content instead.
It is just as effective to respond to a comment right on the blog
It is a turnoff. Commenting on the blog again may result in another email.
This puts pressure on the commentator to subscribe to the blog.
In some respects I have to agree with Jennifer. I have received thank you emails for my comments, but the ones that I dislike are generated by auto-responders.

My philosophy is this: if I take the time to leave a well thought out comment, then I dont want a canned response. Either dont respond at all (hey, I understand that we are all busy), leave a comment back on your blog, or send me a personal email that you took the time to write. I dont expect an email for a comment that I make, but if what I said sticks with you and you want to email me – write it yourself.