When I add a multi-value custom fields to a profile, Civi only allows visitors to enter the fields once - as a simple fields.
How to configure custom fields and profile to get form with multi-field table described in "Multi-value fields in profiles" section on http://book.civicrm.org/user/current/organising-your-data/profiles/
This table with 'new record' in form is also described there http://wiki.civicrm.org/confluence/display/CRM/Multiple-record+Custom+Data+Sets+in+Profiles