I think if a forum topic hasn't been posted on for over a month with a post that contains relevant information, it should be locked and moved in the archives. Looking at the forums I am seeing stuff as early as December for the last post. Some of these topics are also outdated. It would make it easier to find more relevant and current information if we didn't have to filter it.
Edit:
Locked posts should be moved into the archives as well if the information dealing with there topic is no longer relevant or if the topic was meant for a time several months ago.