If you can force the forum to display in the order posted, then why does it matter if a bump puts something at the top of a search based on recent activity? People who want to see a direct list, fairly ordered, can easily, and by default see it. If you allow bumps to be visible in the activity searches, people who really want to see what gear people want to jabber about could have their fun too. Plus, you wouldn't have to waste any time adjudicating wether a post adds something substantial, or is just an empty bump.
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