Feature Request: Custom Activity Stream by Keyword or Phrase

Hello,

 Quite a few of my members have asked me to pass on this recommendation. They say they love the new activity stream feature, but they'd like the ability to add keyword or phrase filters onto streams so they can quickly come back to the site and have a stream that shows all the new content about that specific topic that interests them (e.g. "Mountain biking"). I told them I'd pass on the recommendation, so here it is. 

-Cris