trying out this distributed thing
I don't know if this will work, but an alert if you are replied to anywhere in ZeroNet.
Whenever a site you are seeding is updated, the owner sends it to a few peers, then slowly it proliferates through the network, everyone sending it to someone else.
Now, with comments, it's a bit different. The first time, the comment poster contacts the owner of the site then asks for permission to add content. This permission is given, and the public key of that user is stored on the site. The next time they try to post a comment, it no longer has to go through the owner. It can go straight to the peers. 
So every new comment on every site you are seeding eventually goes through you. The client could check these new comments and see who they are replying to. If it is any of the users on that computer, they can make an alert. If not, nothing happens.
This would not only serve a huge purpose, especially as ZeroNet starts to grow, it would also make the entire network feel very interconnected.
 This is my understanding of it. Please correct me if I'm wrong.