CCK counterpart for user's profiles?
For Drupal 6, these are the only two options I know of, either use content_profile and use aditional nodes or stick with what profile.module can do.

In Drupal 7 however, users are fieldable, which means that you can attach any field that you can attach to nodes too. Additionally, there is the http://drupal.org/project/profile2 project, which provides something similar to content_profile. However, profiles are in that case not nodes but a custom entity.