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.
If you want some other feeds, write me. It is easy to set them up.