Notifications for anonymous users on nodes
I would probably solve this with the following Rules-based setup:

1) Create a custom entity for anonymous posters with only a text field for email and an entity reference field for the node they created. Here's a pretty good writeup on creating custom entities: 
http://www.istos.it/blog/drupal-entities/drupal-entities-part-3-programming-hello-drupal-entity

And here's Drupal.org: http://drupal.org/node/1026420

2) Create a rule for "Node->After saving new content" that checks if the poster was anonymous and if so, creates a new anonymous posters entity with the user's email + reference to the created node.

3) Create a rule for "Comment->After saving a new comment" that does a "Fetch entity by property" action and after a anonymous poster entity, sends an email out to them.

The only trick you need to figure out is how to play with rules upon fetching entities and accessing their fields. You need to create some rules component so achieve this whole flow since in order to access the field in the entity, you need to verify the type of the entity and this happens in "conditions", which can't be done after "actions" which is where the "fetch entity by property" magic happens.

So you'll basically have to create a Rules Component that does what needs to be done with the fetched entity.

This is definitely not the only way to achieve what you need to accomplish, but since I'm a strong believer in the endless powers of Rules, I like solving things with it. :)