Visitors have been commenting on my WPMU blogs for years now. On Saturday afternoon the comment_content started coming in blank for no apparent reason. All of the comments prior to Saturday are unaffected. I logged in to the MySQL database and confirmed the comment_content field is empty the database for recent comments.
What's so bizarre about this problem is no one claims to have changed anything and I've went so far as to restore the comment template from last month and uninstall recaptcha. It didn't help.