There is a plugin that supports two-factor authentication via Google's Authenticator for self-hosted Wordpress blogs. Is there a similar feature I can turn on for hosted wordpress.com blogs? Every search I do turns up the former mechanism...
Two-factor authentication is now available on WordPress.com blogs.
Wordpress.com blogs now supports two-factor authentication both via Google Authenticator as well as SMS.
See Wordpress | Two Step Authentication for an how-to on setting it up.
Considering that the plugin isn't developed by WordPress and you can't install custom plugins on a wordpress.com blog, so no - at the moment there's no way to turn on two-factor authentication for Wordpress.com blogs