If it is not used by anyone else, then we should rename it to
reflect what it does, so it is not ambiguous.
I wonder if this sets a precedence or something about columns
used only by contrib module(s) and possible clashes where one
module thinks it is for X and another thinks it is for Y and they
overwrite each other.
Can't you just create your own table for that module and make
uid the primary key for it? Yes, an extra join, but then that table
is solely yours, and everyone else should keep their grimy hands
off.
Does anyone know if any core module uses the 'mode' column in the
{users} table? A quick search with grep didn't turn up anything so I
was thinking about using it as a flag for per-user behavior for a
custom module for a little site.
-Peter