I refactored quite a bit of the user.module:

$ diffstat user.patch
database/database.mysql |    4
database/database.pgsql |    2
database/updates.inc    |   10 -
modules/block.module    |   20 +-
modules/locale.module   |    9
modules/profile.module  |  108 +++++++----
modules/system.module   |    8
modules/user.module     |  456 +++++++++++++++++++-----------------------------
8 files changed, 289 insertions(+), 328 deletions(-)

More functionality, less code.  Here is a list of the changes:

- Some user API changes:
   + When $type is 'form', you have to return an associative array of groups.  In turn, each group is an array with a 'title', 'data' and 'weight'.
   + A new $type has been added, namely 'categories'.  User settings can be organized in categories.  Categories can be sorted, as can the groups within a category.  (Ordering 'categories' is somewhat broken due to a bug in the menu system.)

- The 'my account > edit' page will use subtabs for each 'category'.  Read: you can break down the account settings into multiple subpages.

- Profile module improvements:
   + Added support for private fields to the profile module!
   + Improved workflow of profile administration pages.
   + Improved the form descriptions.

- Code improvements:
   + Unified user_edit() and user_admin_edit().
   + Unified and cleaned up the validation code.  Fixed some validation glitches too.