Yes. There are multiple options for JFBConnect registration. You can use automatic registration, where the account is automatically created. That's good to get the user in the site quickly, but their details will be automatically generated as you mentioned.
Alternatively, you can use the "Normal" registration process where the user can set their own username and password. There are options to hide username, password, email or other fields that can be automatically generated or imported from Facebook as well, so that, even though there is a form, it could *only* have a "Username" field. That way, you still have a very quick registration process, but get all the info you need to create the account (email comes from Facebook, password is auto-generated, profile info from Facebook), etc.
It's very flexible, and up to you how long, or short, you want the registration form to be.
Hope that helps explain,
Alex