I'd like to have an unlimited number of custom fields connected to users.

It would also be nice to be able to set some fields to be read-only for users, so that admins can update them but not the users themselves.

i actually went the route of adding an auxilliary table:

ubbt_USER_EXTRA, with tonz of fields -- adminable..

this is so that upgrades would never get in the way of any mods using that table

I like SD's input here