When a user subscribes, I understood that their gravatar would be pulled based on their email address. This is not happening, perhaps not right away. What is the delay period for the gravatar for the user to be pulled from gravatar.com?
Ok, there is a lag for Gravatar to expose the user email address. If I try with an email which has been in Gravatar for a long time, it works. So the Gravatar image or additional email addresses need to be registered with Gravatar for probably a few hours.
Second point, its a bit of a shame that we need to register with Wordpress to use GRavatar - but thats not for here.