Thank you, WordPress, for continuously adding useful features such Comment Reply Via Email. I do have a suggestion, though, regarding email signatures.
I'm sure a lot of users have configured their email clients to automatically add a signature to outgoing emails. Some users may not wish to have their signatures included as part of a comment reply. This means they'll have to manually delete a signature in a draft email.
Perhaps WordPress can consider tweaking their servers to recognize the -- that is typically at the start of a signature as the end of the text that goes into a comment reply?
My blog post on this matter here: http://atinyblip.com/2009/05/12/punkd-by-wordpress/