When a post gets old, instead of simply closing the discussion, send comments and trackbacks to the moderation queue. This will greatly reduce spam.
For documentation and tips, please refer to the official plugin page for <a href="http://planetozh.com/blog/archives/2005/02/02/wordpress-plugin-auto-moderate-comments/" title="Auto Moderate Comments" rel="nofollow ugc">Auto Moderate Comments</a>

Ozh' Auto Moderate Comments

When a post gets old, instead of simply closing the discussion, send comments and trackbacks to the moderation queue.

Your feed, on steroids : add a custom footer to RSS items with, for example, a copyright notice, a “Read More (400 words)” links, an “Add to del.icio.us” link, a list of related entries, or anything really (even custom PHP functions). Compatible with Feedburner or similar services.
Improve connectivity between your feed and your site !!
For documentation and tips, please refer to the official plugin page for <a href="http://planetozh.com/blog/my-projects/wordpress-plugin-better-feed-rss/" title="Better Feed" rel="nofollow ugc">Better Feed</a>

Ozh' Better Feed

Your feed, on steroids : add a custom footer to RSS items with, for example, a copyright notice, a "Read More (400 words)" links, an "A …

Ozh' Auto Moderate Comments vs Ozh' Better Feed