Quick question before I consider changing a username - do pulumi accounts using email login (within an organization) have to have a unique username across all of pulumi or just within the org?

Users aren't "within" an organization, they have access to it.

And user names?

Again, users are not "in" an organization. They are just Pulumi users. A single user has a single username, and that user can be associated with any number of organizations. Hence, usernames are Pulumi-wide.

Cheers