One of the features I've wanted on Facebook is the ability to reply to a comment thread from my email. For example, there are often times when I receive a Facebook notification email on my iPhone, where I would rather hit reply than to quit the mail app, open the Facebook app, go to my profile (or wherever else the comment thread was occurring), and then comment. Finally, my requests have been answered.
I have only had a chance to play with this feature a bit. So far, I've replied to the above thread, but cleared out the chain text and my email signature. I don't know if Facebook is smart enough to remove all of the duplicate content from the email, but I'm hoping that it is. Regardless, thank you Facebook team for finally adding this much needed feature. With more and more people on smart phones, you have eliminated several steps when it comes to commenting.