Simia offers a number of RSS feeds to subscribe to:
If you are interested in a certain topic, go to the list of all topics, click on the one you are interested in. On the page you will find a link to subscribe to all posts on this topic. If you are on a particular post, you will see comments. You can subscribe to the comments of those posts on the post's page.
There is also a feed of all changes on this website:
Atom feed of all changes
I would be rather surprised if anyone subscribes to this one :)
If you want some other feeds, write me. It is easy to set them up.