Akismet and other comment watching plugins can help monitor for spam, but a quick way to cut back on spam trackbacks and comments is to close old posts. This is especially important if you are running a large blog or one that has been online for a long time. My favorite way to do this used to be with the plugin simply called Close Old Posts however, this feature has now been integrated into WordPress. Just how do you close old posts?
Within the admin interface navigate down to Settings and then Discussion from the menu on the left (click the image below for a larger version).
Here you will find a checkbox that you can select to close posts. The default time is 14 days but you can change this to whatever number suits you best. I have found that 30 days tends to be the best, less if you update a lot. That gives visitors plenty of time to leave a comment but keeps the conversation from getting stale. Some bloggers and commenters prefer to keep comments on their relevant posts, but if someone just read an article I posted a year ago, I would just prefer them to leave a comment on my most recent post if they don’t feel like shooting me an email.
Since this is a built in WordPress feature you can impliment this in self-hosted WordPress installs as well as on WordPress.com blogs.