I gave up.
Gravatar didn’t read the email I sent them, but they did respond. They told me to do exactly what I’d told them I’d already done.
So I told them that. They emailed back (actually this time within a few minutes) and said try logging into WordPress.com.
So I tried to log into WordPress. No go. First, logging in, I get “No such user.” Then I try to set up a new account and get “That user already exists. Log in.” Try logging in, and I get “No such user.” Try “Forgot password” and enter username, and I get “No such user”. Enter email address and I get “No such email address in the system.”
Back to the logic that surely No Such User means I can create that user account. Nope. That user already exists. “Did you forget your password?”
By now there’s enough of my hair on the floor to donate to Susan’s hair donation lens.
So I gave up and entered a different username to sign up with. And voila! Activate the link, open up Gravatar and I’m already signed in under that name. Upload an avatar, open SquidTop, refresh a couple of pages… and here I am. Under the wrong username, but at this stage who gives a continental two-bit hoohah.