I we helping someone debug their gravatar recently. There was a long back and forth about your WordPress.com vs WordPress.org account when he couldn’t log in, and once we sorted that, we wanted a way to check if the Gravatar was actually working. Lo! There’s an easy way:
You can put in anyone’s email and get their Gravatar, which is a great check for people on, say, WordPress.org complaining theirs isn’t working when it totally is, had they used the right email.
There are some things I wish Gravatar had, though, like the ability to drag-and-drop new avatars instead of the old click-here-to-select interface that feels so very, very, old now.