New Online Game I'm playing - called 'Comment Spam Bingo'

I'm still getting hit with comment spam, not on the new posts (because I disabled comments) but on the old ones that I haven't gone back and closed down comments on. I've got a new tactic. As I get the comment spam I go to the old post and mass delete all of the spam comments for that post and then close the comments. In one fell swoop I solve the problem for that particular post.

I'm not going to go through the trouble of disabling comments for all posts. I'm going to wait until each one gets hit and then delete the spam comments and then close further comments. When the last post gets hit and then disabled I'm going to announce "Comment Spam Bingo!"

Update: I like David Sifry's idea of cutting off comments that are more than a week old. I can't implement this with TypePad, but maybe the folks at TypePad can make it happen. Most legitimate comments are made within a week of the post, and most spam comments only show up on posts that are over a couple of weeks old. So this is probably the best solution.