Custom profile categories are added below the standard profile edit screen. They can be re-ordered within themselves, but always appear en-masse below the main edit fields. If there are a large number of custom fields/categories this does not make for good usability as the form becomes very long.
This feature would split each of the custom categories onto a separate tab so that they can be edited and saved separately to the main user profile. On clicking the "edit profile" button, the main profile screen would be displayed. There would be tabs at the top of the screen, and links in the navigation block, to access the custom category forms. Custom categories would appear in order (left to right) as defined in the custom profile field administration.
Each custom category tab would have an independent "update profile" button. If a user makes changes but switches tabs without pressing the "update profile" button, their changes will be lost.
Question: this could/should be optional - admins maybe would want to decide whether to go for a long form or tabs.
I have a number of requests for this (for our Sept 2011 release) and am more than happy to program myself and offer a patch. If whoever triages this thinks that's OK, please assign to me and I will add to the OU development schedule over the next few months.