Bumping old topics is looked down upon. If there's a topic that's been active within the past month, I'd say it's fair game to give it a bump, but after that, I'd say you're better off making a new topic, so long as you have legitimate reason for doing so.
If you're going to revive an old topic, or make a new one just to respond to someone's comment, or say something that's already been said, you're wasting everyone's time.
