View One: Phil's perspective found in
http://www.arsdigita.com/books/panda/
is to initially just get the Name and Email address.
Later when the person is more familiar with the community
you can ask for more information.
Another reference regarding Usability that I like is Dr. Jakob Nielsen:
http://www.useit.com/alertbox/
View Two: Perhaps you are asking about other fields that
you can ask the user to fill in. See the fields in the user_contacts table.
View Three: (Some humor)--- Pay the user to fill in the info or give them something. 😊
-Bob