@cyberczar I disagree! The explicit point of the bangtag is to put stuff into the home timeline (and thus bump up the thread) of members in a group with a collective interest.
And having wildly different behaviour is counterproductive, consider: "weell, this is a post that belongs to a thread already part of a conversation in group A so I shouldn't bump it up, but maybe I should bump it up if it's been a week since the last post but maybe sometimes that time limit should just be a day and maybe some members don't actually want posts from the group even though they're part of it..."

The simplest solution is often the best:
* Use bangtags when the specific post is relevant to the interest of members in the group.
* If not, and we just want to categorize the post, use ordinary hashtags.