There are several rss feeds throughout the site.

To get a feed of the latest posts:
http://talk.rubynow.com/rss/posts

To get a feed of the latest threads:
http://talk.rubynow.com/rss/threads

To get a feed of all new posts under a particular tag, use the url:
http://talk.rubynow.com/rss/tag/ + tag
So to get all the newest tags for drb, use http://talk.rubynow.com/rss/tag/drb

To get feeds for a specific user, just use this url: http://talk.rubynow.com/rss/user/ + username
So if you wanted to get the rss feed for jtoy, just use http://talk.rubynow.com/rss/user/jtoy

If you want to get a feed for a particular tag for a person, just add the tagname to the end of url, so for jtoy's drb tag, you would use:
http://talk.rubynow.com/rss/user/ + jtoy + / + drb
which would look like:
http://talk.rubynow.com/rss/user/jtoy/drb