Upgraded a site from 2.3.1 beta to 2.4.1 last night. I tested out the registration and everything worked, except when I tried to register a user with the same email as an existing user. I got the standard red error that the email address was already registered BUT the activation email was still sent. When I clicked the link in that email I got: "Selected account is already activated."

Not a giant problem, but still strange.