Please upgrade to 2.2 here.
The 2.0 and 2.1 branches are no longer being updated.
EMailSubscription using bookmarks
I was having an issue with this plugin and I had to take a look at your code to find the problem.
Your addon lets you subscribe to new conversations but uses the bookmark feature to subscribe to conversations in an ongoing manner.
I can see why you did this but unfortunately it will not work in my case. I've migrated a ton of old forum data over from an older Vanilla 1 forum, and I don't want to have to go bookmark every conversation in a discussion in order to get notified of new comments.
Instead of hooking the new conversation save method, can you hook the new comment method (or both) to provide a way to monitor ALL comments in a category?