BuddyPress.org

Generating the username from the email address is not ideal, because it’s also used for the blog URL – if you allow creation of blogs.

My first thought would be to generate username from the full name. Or leave the username field on the registration form, but rename it as “blog name” and move it down on the form.

Or a combination of both where the username/blog name field is not visible when you first register and you get a suggested blog name based on your real name when you register a blog.