You can get reply notifications (email or mobile) using Notifo (YC W10)[1]. I think it's only for replies to your comments, not for all activity in a thread.

You can get reply notifications (email or mobile) using Notifo (YC W10)[1]. I think it's only for replies to your comments, not for all activity in a thread. [1]: http://news.ycombinator.com/item?id=1720763