I think it would be quite helpful to use the Hashtags page to allow group members to mute or un-mute various hashtags. Each hashtag box should have a button at the bottom to "mute this hashtag" or "Un-Mute this hashtag" (depending on its current state for the user). This would achieve several things. 1) easy to see which hashtags you have muted (maybe even including the remaining duration of the mute), 2) easy for a new member to scan through the list of hashtags and mute those that are of no interest to them, and 3) allow a central place on the web interface to add/remove hashtag muting.
