Threaded Comments in Blogger ...for your face!
Also, do not think for a second that the irony of how frequently I post here about comments and the fact that no one ever comments here has been lost. It is not, trust me.
In order for this to work on your blog make sure your post feed is set to "full" and your comment form is set to "embedded".
For more information on this new update visit the Blogger Buzz.
Update: People are saying they are having difficulty getting this working on customized templates. Visit this thread at Blogger help for some possible fixes.