I'm thinking that IWE used to have a good approach to archiving. Just setup a target archive page with the forum link moved from the main page onto the archive page. One thing that would be nice is to have the URL for the individual messages not change based on being archived or active - just keep the same forum id. Just keep 'em semi-categorized and datestamped on the archive access page.
An additional question along these lines is whether the permanent forums (Open, Pun, etc...) should be periodically archived off and a fresh forum started. I'm sure all of our first post advocates will need little encouragement along these lines. :-)