On a few occasions I had to check if a column was the primary key (with auto-increment) in a table. One of these occasions was when I wanted to automate the creating/updating of a row after a form has been submitted and validated. The identity column needed to be ignored, because a value shouldn't be explicitly set. I ended up writing the following method in a custom Zend_Db_Table class:

public function isIdentity($column)
{
    if (!isset($this->_metadata[$column])) {
        return false;
    }

    return (bool) $this->_metadata[$column]['IDENTITY'];
}

I'd like to see this method added to Zend_Db_Table_Abstract if possible for 1.5 :)