Repeating text field on user profile
If you're working in Drupal 7, check out the Field Groups Module. 


  Fieldgroup will, as the name implies, group fields together. All
  fieldable entities will have the possibility to add groups to wrap
  their fields together. Fieldgroup comes with default HTML wrappers
  like vertical tabs, horizontal tabs, accordions, fieldsets or div
  wrappers.


If you're on Drupal 6, you want the MultiGroup module, which is a part of the 3.x branch of CCK.