Fbconnect_profile has been removed by the maintainer. See: http://drupal.org/node/487936
If you enable the bundled Fbconnect Profile module you will be able to import a users profile information in to your Drupal site when they register.
The Facebook profile data is updated every time the user re-authenticates with your Site. if they do not return after 24 hours the imported data is deleted. This is in line with the Facebook terms of service.
You can define what information you wish to collect about a Facebook user on the /admin/settings/fbconnect settings page.
A series of checkboxes are provided. Anything you tick will be listed to the users signing up to your Drupal site. They have to agree to the information being made available to your Drupal website too.