Act on user objects when loaded from the database.
Due to the static cache in user_load_multiple() you should not use this hook to modify the user properties returned by the {users} table itself since this may result in unreliable results when loading from cache.
$users: An array of user objects, indexed by uid.
Note: this list is generated by pattern matching, so it may include some functions that are not actually implementations of this hook.
function hook_user_load($users) {
$result = db_query('SELECT uid, foo FROM {my_table} WHERE uid IN (:uids)', array(
':uids' => array_keys($users),
));
foreach ($result as $record) {
$users[$record->uid]->foo = $record->foo;
}
}