In version 3 of the CCK ( Content Construction Kit ) module that is currently under development, they have included a module called Content Multigroup that basically allows us to make a group of fields that can be added dynamically by the user.
Remember that in version 2 we can tell a field that the allowed quantity can be unlimited and it is very useful for uploading images or other information of which we want to allow an unspecified quantity, the same concept is the one that allows Content Multigroup only applied to a group of fields. Example: You have a group of fields that define all the studies for your resume, one field says what year you graduated, another from what school and another the degree you obtained, but what if you need a person to be able to add all your studies regardless of how many there are and in each one fill out those three fields? You should have a way to add that group of fields again dynamically as many times the user needs it, for this case Multigroup is the solution.
I just implemented it in a project and it works very well, surely more than one of you had this problem and will remember that the only way we had was to design the interactivity in pure code with the help of AHAH.