I like the idea. I just made a quick test (visible here: http://www.resubj.com/inboxes/1152) to look at the code formatting. The formatting looks great for Ruby, but not-so-much for Lisp. Not a huge issue, but maybe when somebody clicks the programmer? link, it'll show a list of supported languages.

The email that I got was in plain text. Maybe there could be an option when creating the message to send the emails with formatting? That way, if you know that your friends can see formatted emails, you can send properly colored code.

Comment posting is very quick. When I sent in a comment through email, it took about half a minute for the comment to show up -- but I guess that's to be expected.

So, my general verdict:

I like the idea.

However, I think that for it to appeal to non-hackers, it should support formatting. It could even be something simple, like the italics supported by HN.