We started getting a spam registration a minute – granted, only for a couple minutes – but it was still worrying enough to look for some anti-spam firepower.
drush dl mollom
Push the changes to our live site.
Enable Mollom at admin/modules.
Register the site at Mollom.com.
Copy the API keys for public and private to the Mollom settings page on our site, admin/config/content/mollom/settings
hmm. It tells us "The configured Mollom API keys are invalid."
Check the Mollom issue queue (http://drupal.org/project/issues/mollom) to see if anyone else is being told valid keys are invalid.
Since no one else is having this problem, it's probably not the module but our Mollom account. We send a polite e-mail to Mollom reporting this problem.