profile form should hide categories that contain only hidden fields

profile lets the admin define some profile fields as 'hidden', which is great --
but if those profile fields have a category, the category tab isn't hidden at all.
instead, it gives a blank form.

perhaps profile should let you define a whole category as 'hidden' and then
the profile_user('category', ...) hook could determine the context and return
only what should be seen.

or else maybe user_edit needs to do a db query to check each category and
determine whether it should be shown in the current context.

or else some other thing. i'm not a developer, i just play one on the internet.