Thanks for this. Collapsible comments are one of the two biggest things I miss from reddit when on HN (the other being some form of notification that someone has replied to you).
To be notified when someone replies to me I use Notifo (http://notifo.com/) and put my Notifo username in my HN profile. I don't think you need a mobile device to use Notifo, you can install a desktop app that provides notifications when you get a reply. http://notifo.com/desktop
I think I'd prefer a desktop app over email. I don't get a lot of replies here, largely due to my infrequent commenting, but I'd hate to randomly hit upon a popular comment and be flooded with 20 emails while I'm out.
