I can't speak for him, but the RSS reader I am working on at the moment is simil...

I can't speak for him, but the RSS reader I am working on at the moment is similarly split into multiple parts:

* Crawler - retrieves RSS feeds and parses articles

* Database server

* Analyser - performs semantic analysis and various other statistical processing on posts

* Propagator - pushes new posts to everyone's feed

* Cacher - serves a cached copy of the user's feed

* Web server

Based on loads I would just add more nodes depending on what was needed.