planet.jboss.org does not relies on tag specific feeds. It does require the tag info to be in the feed to filter things out. But Awestruct does that (or the improvements I built upon).

To be honest, I'd just start with a global feed with only the posts. Ignore comment feeds since it's easier to follow them directly from Disqus. If we see the need for a per tag feed, we can work on it but yes it does add extra computation that we should avoid.