I’ve closed comments on posts older than 90 days in attempt to keep up with spam.
My blog is nowhere near as popular (or good) as Popehat, where I got the idea, but I was still dealing with upwards of 300+ spam messages a day in the filter. Comments on posts older than 90 days have been closed since Monday, and I’ve seen about a 2/3rds decrease.
If you do want to leave a comment on an older post, you’re more than welcome to use the “Contact the proprietor” link and drop me an email.